Code Oz

Posted on Nov 18, 2021 • Updated on Dec 2, 2021

You MUST store this Javascript Operator Index

#javascript #webdev #beginners #codenewbie

Here is a list of javascript operator and how to use it!

You should mark this and use it when you need to know what is this operator!

In order to naviguate, you can make a cmd + f or ctrl + f and put the operator that you need and put : after this.

Example: ...: if I'm looking for what is ... operator

🚨 Popularity is defined by my OWN usage.

Ambidextrous operator

`+`: addition | unary plus

Popularity: ★★★★☆

If you use `+` operator BEFORE operand, it will be used as `unary plus operator`.

The unary plus operator precedes its operand and evaluates to its operand but attempts to convert it into a number, if it isn't already.

const x = 1
const y = -1

console.log(+x)
// expected output: 1

console.log(+y)
// expected output: -1

console.log(+'')
// expected output: 0

console.log(+true)
// expected output: 1

console.log(+false)
// expected output: 0

console.log(+'hello')
// expected output: NaN

📝 Note: If you try to use it with a string that is not a number, it will return NaN (not a number)

If you use `+` operator in other context will be used as `addition operator`.

It Produces the sum of numeric operands except for string

📝 Note: It will convert boolean to number, object to number

console.log(2 + 4) // 6
console.log(2 + true) // 3

When you use it with string it will make a string concatenation

const name = 'code oz'
console.log('hello ' + 'my name is ' + name)

📝 Note: you should use template litterals string instead of concatenation

`-`: subtraction | unary negation

Popularity: ★★★★☆

If you use `-` operator BEFORE operand, it will be used as `unary negation operator`.

The unary negation operator precedes its operand and negates it.

📝 Note: It will convert boolean to number, object to number & string to number

const a = 5
console.log(-a) // -5
console.log(-'1') // -1

📝 Note: If you try to use it with a string that is not a number, it will return NaN (not a number)

If you use `-` operator in other context will be used as `subtraction operator`.

It subtracts the two operands, producing their difference.

console.log(5 - 3)
// expected output: 2

console.log(3.5 - 5)
// expected output: -1.5

console.log(5 - 'hello')
// expected output: NaN

console.log(5 - true)
// expected output: 4

`...`: spread | rest

Popularity: ★★★★☆

If you use `...` operator as function argument during execution, it will turns array into a list of arguments. In this context it's called `Spread operator`.

let arr = [3, 5, 1]

Math.max(...arr) // 5 (spread turns array into a list of arguments)

You can use `...` operator in another way that is the `opposite of turning array into a list`, it's when you convert `some item into an array`!

It allows us to have an unlimited number of parameter for this function! since it will convert the arguments (list of item) into an array that is the argument!

// rest parameter is handle as array in the function
const add = (...rest) => {
   return rest.reduce((total, current) => total + current)
}

// Nice your function can handle different number of parameters !
add(1, 2, 3)
add(1, 2, 3, 4, 5)

You can also use it for extracting values from array or object

// We extract the first Item of the array into the variable and the others variable in an array named others
const [ firstItem, ...others ] = [ 1, 2, 3, 4 ]
firstItem // 1
others // [ 2, 3, 4 ]

const toto = { a: 1, b: 2, c: 3 }
const { a, ...others } = toto
a // 1, we extract the a key from toto object
others // { b: 2, c: 3 }, we extract other key in the object thanks to rest operator

📝 Note: When you are doing const toto = { ...anotherObject } it's equal to const toto = Object.assign({}, anotherObject)

Summarize:

Spread operator: Transform arrays into list of arguments.

Rest operator: Transform list of arguments into an array.

Logical operator

Thing to know: All value in Javascript are falsy or truthy value, it means that you can make Boolean(any value), and you will get boolean value. In Javascript all value are truthy value except 0, null, undefined, NaN, empty string

`&&`: logical AND

Popularity: ★★★★★

Use to check if all value (in general value are condition) are truthy.

It will return the first value falsy, otherwise it will return the final value.

const isTrue = true
const isFalse = false


const value = isFalse && isTrue // will return false 
const valueBis = isTrue && isFalse // will return false

const toto = 5 && 3 && 1 // will return 1 since all value before are true (5 & 3)

const tutu = 5 && 0 && 2 // will return 0 since it's the first falsy value

if (firstCondition && secondCondition) { console.log('hello') } // console log will be shown only if both condition are true!

`&&=`: logical AND assignement

Popularity: ★☆☆☆☆

Value is assigned only if value passed is truthy.

let toto = 0
let tutu = 2

toto &&= 5 // toto value will be NOT changed since toto is falsy (0)
tutu &&= 3 // tutu value will be replaced by 3 since tutu is trusly (2)

// toto &&= 5 It's a shortcut of 👇

let toto = 0 

toto = toto && 5

`||`: logical OR

Popularity: ★★★★☆

Use to check if one value (in general value are condition) are truthy among a set of value.

It will return the first value truthy, otherwise it will return the final value.

const isTrue = true
const isFalse = false

const value = isFalse || isTrue // will return true 
const valueBis = isTrue || isFalse // will return true

const toto = 5 || 3 || 1 // will return 5 since it's the first truthy value

const tutu = 0 || 2 || 5 // will return 2 since it's the first truthy value

if (firstCondition || secondCondition) { console.log('hello') } // console log will be shown if one condition matches!

`||=`: logical OR assignement

Popularity: ★☆☆☆☆

Value is assigned only if value passed is falsy.

let toto = 0
let tutu = 2

toto ||= 5 // toto value will be replaced by 5 since toto is falsy (0)
tutu ||= 3 // tutu value will NOT changed since tutu is not a falsy value (2)

// toto ||= 5 It's a shortcut of 👇

let toto = 0 

toto = toto || 5

`??`: logical Nullish Coalescing

Popularity: ★★★☆☆

Returns its its right-hand side operand when its left-hand side operand is null or undefined (nullish value).

const toto = 0 ?? 55 // 0 since 0 is not equal to nullish value.
const tutu = null ?? 'hello' // 'hello' since the right-hand side is equal to `null`
const tata = undefined ?? 55 // '55 since the right-hand side is equal to `undefined`
const titi = null ?? undefined // undefined since the right-hand side is equal to `null`

⚠️ Be careful: ?? operator is different of ||, so when you need to assign a value depending on other value, you should pick the correct operator!

const toto = 0 || 55 // 55 since 0 is a falsy value
const titi = 0 ?? 55 // 0 since 0 is different of nullish value

const tutu = undefined || 55 // 55 since undefined is a falsy value
const tata = undefined ?? 55 // 55 since undefined is equal to nullish value

`??=`: logical Nullish assignement

Popularity: ★☆☆☆☆

Value is assigned only if value passed is equal to null or undefined (nullish).

let toto = null
toto ??= 55 // toto is equal to 55 since it's a nullish value (null)

let tutu = 90
tutu ??= 23 // toto is equal to 90 since it's not a nullish value (90)
// toto ??= 5 It's a shortcut of 👇

let toto = null

toto = toto ?? 5 // Equal to 5 since toto is equal to null

`!`: logical NOT

Popularity: ★★★★★

Swap a true value into false value and false value into true value.

It also convert any value to boolean value. So all truthy value become falsy value and vice versa.

💡 Tips: I use double logical operator a lot in order to convert any value to boolean! It's equal to use Boolean(any value)

console.log(!true) // false
console.log(!true) // true
console.log(!0) // false
console.log(!1) // true

console.log(!{}) // false
console.log(![]) // false
console.log(!undefined) // true

// My tips 👇
console.log(!!{}) // true, equal to Boolean({})
console.log(!![]) // true, equal to Boolean([])

if (!!value) { ... } // I use a lot in order to check if a value is defined or undefined! (Be careful, if the value is equal to `0` it will be false!)

Special operator

`?.`: Optional chaining

Popularity: ★★★★☆

It allows to accesses a property on an object without having to check if each reference in the chain is valid.

It's not really clear? Ok let's have a look 👇

const toto = { a: { b: 5 } }
toto.a // { b: 5 }
toto.a.b // 5
toto.a.b.c // undefined
toto.a.b.c.d // Uncaught TypeError: Cannot read properties of undefined

In fact in you try to access to a property on an undefined property, Javascript engine will trigger an error!

So to be safe we need to make something like 👇

const toto = { a: { b: 5 } }

if (toto.a && toto.a.b && toto.a.b.c && toto.a.b.c.d) {
    console.log(toto.a.b.c.d) // It's safe to use it since we check before if the property exist!
}

But it's not really convenient to make this, isn't?

So opional chaining is here to save us! 🦸‍♂️

You can try to access to a property without check if all property exist before as show above! You just need to use this operator on property, if the property doesn't exist, it will return undefined.

const toto = { a: { b: 5 } }
toto?.a?.b // 5
toto?.a?.b?.c?.d // undefined

`?`: Ternary

Popularity: ★★★★☆

Is the only operator in Javascript that requires two pseudo operand (? and :). It evaluate a condition depending on whether that condition is falsy or truthy! It's equivalent to if (...) & else (...).

console.log(true ? 55 : 10) // 55
console.log(0 ? 13 : 34) // 34

const toto = 2 > 1
console.log(toto ? 'ok' : 'not ok')

//  It's a shortcut of 👇

if (toto) {
    console.log('ok')
} else {
    console.log('not ok')
}

Comparator operator

`==`: Equality

Popularity: ★☆☆☆☆

It checks whether its two operands are equal, returning a Boolean result. Unlike the === (strict equality operator), it attempts to convert (make an implicit coercion) and compare operands that are of different types.

📝 Note: The mechanic of implicit coercion is not easy to understand but you can check it in details at this post https://dev.to/codeozz/implicit-coercion-in-javascript-neh

Here an exemple of how the implicit corecion is done! 👇

// 1) Not the same type so implicit coercion will be made
'24' == 24

// 2) Convert string into number so 
Number('24') == 24

// 3) We got an number so we can check value
24 == 24 // true !

In general you should use === (strict equality) and avoid this operator!

`===`: Strict Equality

Popularity: ★★★★★

It checks whether its two operands are equal, returning a Boolean result. Unlike the == (equality operator), the strict equality operator always considers operands of different types to be different.

console.log(1 === 1)
// expected output: true

console.log('hello' === 'hello')
// expected output: true

console.log('1' ===  1)
// expected output: false

console.log(0 === false)
// expected output: false

You should always use this operator instead of == (equality operator)!

`!=`: Inequality

Popularity: ★☆☆☆☆

It checks whether its two operands are not equal, returning a Boolean result. Unlike the !== (strict inequality operator), it attempts to convert and compare operands that are of different types.

console.log(1 != 1)
// expected output: false

console.log('hello' != 'hello')
// expected output: false

console.log('1' !=  1)
// expected output: false

console.log(0 != false)
// expected output: false

In general you should use !== (strict inequality) and avoid this operator!

`!==`: Strict Inequality

Popularity: ★★★★★

It checks whether its two operands are not equal, returning a Boolean result. Unlike the (!= inequality operator), the strict inequality operator always considers operands of different types to be different.

console.log(1 !== 1)
// expected output: false

console.log('hello' !== 'hello')
// expected output: false

console.log('1' !==  1)
// expected output: true

console.log(0 !== false)
// expected output: true

You should always use this operator instead of != (inequality)!

`>`: Greater than

Popularity: ★★★★☆

It returns true if the left operand is greater than the right operand, and false otherwise.

console.log(5 > 3)
// expected output: true

console.log(3 > 3)
// expected output: false

console.log('ab' > 'aa')
// expected output: true

`>=`: Greater than or Equal To

Popularity: ★★★★☆

It returns true if the left operand is greater than or equal to the right operand, and false otherwise.

console.log(5 >= 3)
// expected output: true

console.log(3 >= 3)
// expected output: true

console.log('ab' >= 'aa')
// expected output: true

`<`: Less than

Popularity: ★★★★☆

It returns true if the left operand is less than the right operand, and false otherwise.

console.log(5 < 3)
// expected output: false

console.log(3 < 3)
// expected output: false

console.log('aa' < 'ab')
// expected output: true

`<=`: Less than or Equal To

Popularity: ★★★★☆

It returns true if the left operand is less than or equal to the right operand, and false otherwise.

console.log(5 <= 3)
// expected output: false

console.log(3 <= 3)
// expected output: true

// Compare bigint to number (note: bigint is not supported in all browsers)
console.log(3n <= 5)
// expected output: true

console.log('aa' <= 'ab')
// expected output: true

Arithmetic operator

`+=`: Addition Assignment

Popularity: ★★★☆☆

Adds the value of the right operand to a variable and assigns the result to the variable.

let a = 5
let b = 3

b += a // b will be equal to 8, since we are adding 5 to b variable!

`-=`: Subtraction Assignment

Popularity: ★★★☆☆

Subtracts the value of the right operand to a variable and assigns the result to the variable.

let a = 5
let b = 3

b -= a // b will be equal to 2, since we are subtracting 5 to b variable!

`*`: Multiplication

Popularity: ★★★☆☆

Its produces the product of the operands.

let a = 5
let b = 3

let c = a * b // 15

`*=`: Multiplication Assignment

Popularity: ★★★☆☆

Multiple the value of the right operand to a variable and assigns the result to the variable.

let a = 5
let b = 3

b *= a // 15

`/`: Division

Popularity: ★★★☆☆

Its produces the quotient of its operands where the left operand is the dividend and the right operand is the divisor.

let a = 10
let b = 2

let c = a / b // 2

console.log(1 / 0) // Infinity

`/=`: Division Assignment

Popularity: ★★★☆☆

Divide the value of the right operand to a variable and assigns the result to the variable.

let a = 10
let b = 2

b /= a // 2

``: Exponentiation**

Popularity: ★★★☆☆

Its returns the result of raising the first operand to the power of the second operand. It is equivalent to Math.pow, except it also accepts BigInts as operands.

let a = 10
let b = 2

let c = a ** b // 100, it equals to 10^2 or Math.pow(10, 2)

`=`: Exponentiation Assignment**

Popularity: ★★★☆☆

It raises the value of a variable to the power of the right operand.

let a = 10
let b = 2

b **= a // 1024, it equals to 2^10 or Math.pow(2, 10)
a **= b // 100, it equals to 10^2 or Math.pow(10, 2)

`%`: Remainder (modulo)

Popularity: ★☆☆☆☆

Its returns the remainder left over when one operand is divided by a second operand. It always takes the sign of the dividend.

let a = 10
let b = 3

let c = a % b // 1

More information about modulo in mathematic -> https://simple.wikipedia.org/wiki/Modulo_operation

`%=`: Remainder Assignment

Popularity: ★☆☆☆☆

It divides a variable by the value of the right operand and assigns the remainder to the variable.

let a = 10
let b = 3

a %= b // 1 it's equal to a % b

More information about modulo in mathematic -> https://simple.wikipedia.org/wiki/Modulo_operation

`++`: Increment

Popularity: ★★★☆☆

It increments (adds one to) its operand and returns a value.

You can use it in two ways:

As pre increment: It increment the value before the operation

let toto = 55

console.log(toto) // 55
console.log(++toto) // 56
console.log(toto) // 56

As post increment: It increment the value after the operation

let toto = 55

console.log(toto) // 55
console.log(toto++) // 55
console.log(toto) // 56

`--`: Decrement

Popularity: ★★★☆☆

It decrement (subtracts one to) its operand and returns a value.

You can use it in two ways:

As pre decrement: It decrement the value before the operation

let toto = 55

console.log(toto) // 55
console.log(--toto) // 54
console.log(toto) // 54

As post decrement: It decrement the value after the operation

let toto = 55

console.log(toto) // 55
console.log(toto--) // 55
console.log(toto) // 54

Bits operator

`&`: Bitwise AND

Popularity: ★☆☆☆☆

Returns a 1 in each bit position for which the corresponding bits of both operands are 1s.

⚠️ Be careful: Don't be confused between & and && operator! The && is the logical operator AND

const a = 5        // 00000000000000000000000000000101
const b = 3        // 00000000000000000000000000000011

console.log(a & b) // 00000000000000000000000000000001

💡 Tips: If you need to check if a number is even, you can use numberVar & 1, if the result is equal to 0, your number is even!

`&=`: Bitwise AND assignment

Popularity: ★☆☆☆☆

It uses the binary representation of both operands, does a bitwise AND operation on them and assigns the result to the variable.

let a = 5      // 00000000000000000000000000000101
a &= 3         // 00000000000000000000000000000011

console.log(a) // 00000000000000000000000000000001

`~`: Bitwise NOT

Popularity: ★☆☆☆☆

It inverts the bits of its operand. Like other bitwise operators, it converts the operand to a 32-bit signed integer

const a = 5     // 00000000000000000000000000000101
const b = -3    // 11111111111111111111111111111101

console.log(~a) // 11111111111111111111111111111010
// expected output: -6

console.log(~b) // 00000000000000000000000000000010
// expected output: 2

`|`: Bitwise OR

Popularity: ★☆☆☆☆

It returns a 1 in each bit position for which the corresponding bits of either or both operands are 1s.

const a = 5        // 00000000000000000000000000000101
const b = 3        // 00000000000000000000000000000011

console.log(a | b) // 00000000000000000000000000000111
// expected output: 7

`|=`: Bitwise OR assignment

Popularity: ★☆☆☆☆

It uses the binary representation of both operands, does a bitwise OR operation on them and assigns the result to the variable.

let a = 5      // 00000000000000000000000000000101
a |= 3         // 00000000000000000000000000000011

console.log(a) // 00000000000000000000000000000111
// expected output: 7

`^`: Bitwise XOR

Popularity: ★☆☆☆☆

It returns a 1 in each bit position for which the corresponding bits of either but not both operands are 1s.

const a = 5        // 00000000000000000000000000000101
const b = 3        // 00000000000000000000000000000011

console.log(a ^ b) // 00000000000000000000000000000110

`^=`: Bitwise XOR assignment

Popularity: ★☆☆☆☆

It uses the binary representation of both operands, does a bitwise XOR operation on them and assigns the result to the variable.

let a = 5      // 00000000000000000000000000000101
a ^= 3         // 00000000000000000000000000000011

console.log(a) // 00000000000000000000000000000110
// expected output: 6

`<<`: Left shift

Popularity: ★☆☆☆☆

Shifts the first operand the specified number of bits to the left. Excess bits shifted off to the left are discarded. Zero bits are shifted in from the right.

const a = 5         // 00000000000000000000000000000101
const b = 2         // 00000000000000000000000000000010

console.log(a << b) // 00000000000000000000000000010100
// expected output: 20

`<<=`: Left shift assignment

Popularity: ★☆☆☆☆

Moves the specified amount of bits to the left and assigns the result to the variable.

let a = 5 // 00000000000000000000000000000101

a <<= 2   // 00000000000000000000000000010100

console.log(a)
// expected output: 20

`>>`: Right shift

Popularity: ★☆☆☆☆

Shifts the first operand the specified number of bits to the right. Excess bits shifted off to the right are discarded. Copies of the leftmost bit are shifted in from the left.

Since the new leftmost bit has the same value as the previous leftmost bit, the sign bit (the leftmost bit) does not change. Hence the name "sign-propagating".

const a = 5          //  00000000000000000000000000000101
const b = 2          //  00000000000000000000000000000010
const c = -5         // -00000000000000000000000000000101

console.log(a >> b)  //  00000000000000000000000000000001
// expected output: 1

console.log(c >> b)  // -00000000000000000000000000000010
// expected output: -2

`>>=`: Right shift assignment

Popularity: ★☆☆☆☆

Moves the specified amount of bits to the right and assigns the result to the variable.

let a = 5      //  00000000000000000000000000000101

a >>= 2        //  00000000000000000000000000000001
console.log(a)
// expected output: 1

let b = -5     // -00000000000000000000000000000101

b >>= 2        // -00000000000000000000000000000010
console.log(b)
// expected output: -2

`>>>`: Unsigned Right shift

Popularity: ★☆☆☆☆

Shifts the first operand the specified number of bits to the right. Excess bits shifted off to the right are discarded.

Zero bits are shifted in from the left.

The sign bit becomes 0, so the result is always non-negative. Unlike the other bitwise operators, zero-fill right shift returns an unsigned 32-bit integer.

const a = 5          //  00000000000000000000000000000101
const b = 2          //  00000000000000000000000000000010
const c = -5         // -00000000000000000000000000000101

console.log(a >>> b) //  00000000000000000000000000000001
// expected output: 1

console.log(c >>> b) //  00111111111111111111111111111110
// expected output: 1073741822

`>>>=`: Unsigned Right shift assignment

Popularity: ★☆☆☆☆

Moves the specified amount of bits to the right and assigns the result to the variable.

let a = 5 //  00000000000000000000000000000101

a >>>= 2  //  00000000000000000000000000000001
console.log(a)
// expected output: 1

let b = -5 // -00000000000000000000000000000101

b >>>= 2   //  00111111111111111111111111111110
console.log(b)
// expected output: 1073741822

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Top comments (15)

Sean May • Nov 18 '21 • Edited

A couple of thoughts, one technical and one subjective:

the ... on the left-hand-side of an assignment statement is also a "rest" operator. "spread" is for expressions (or rhs in statements). When you are putting a bunch of stuff into something, it's a "spread". When you are pulling a bundle of stuff out of something, and giving that bundle a new name, it's a "rest". In functions you are pulling the bundle out of the arguments array
const f = (x, y, z, ...extraDimensions /*rest of the args*/) => {};
const [x, y, z, ...extraDimensions /*rest of the array*/] = dimensions;
const { x, y, z, ...extraDimensions /*rest of the object*/} = dimensions;
I personally feel you should be using ?? at least as often as you are using ?., if not more often. Again, this is the subjective opinion. If you are often using ?. that means you are often getting undefined. If you are passing undefined around, it means that you are often forcing other people (or other parts of the codebase) to do null checking. If you are handling those missing holes in your data with ??, then you have fewer reasons to use ?. farther down the line... Null checking is Sir Tony Hoare's "Billion-Dollar Mistake" and is generally better handled on the outskirts of a system, near the I/O, rather than in the middle of all of the logic... the opinion might be subjective, but it's got a pretty sound backing, by even the inventor of Null (or the person who introduced the concept to programming languages), let alone language researchers.