There are many javascript array mehthods but we will discuss only the following:
- Map
- Reduce
- Filter
- Some
- Every
Map
This method will executes the callback function on each element of the array.
array.map((item, index, array) => {}, thisValue)
Now lets have a look at the usage of the map method:
const names = ["John", "Jane"];
const greetings = names.map((name, index) => {
console.log(index);
return `Hi, ${name}`;
});
console.log(greetings);
Executing above code will output the following:
0, 1
[ "Hi, John", "Hi, Jane" ]
Reduce
This method will reduce the array into one element.
const numbers = [1, 2, 3];
const total = numbers.reduce((total, currentValue) => total + currentValue);
console.log(total);
Executing above code will output the following:
6
Filter
This method will extract all the elements from the array which passed the provided condition inside call back function.
const users = [
{
name: 'John',
isActive: true,
},
{
name: 'Alice',
isActive: false,
},
{
name: 'Bob',
isActive: true,
},
];
const activeUsers = users.filter(user => user.isActive);
console.log(activeUsers);
Executing above code will output the following:
[
{
"name": "John",
"isActive": true
},
{
"name": "Bob",
"isActive": true
}
]
Some
This method will return true if one element passed the condition otherwise it will return false.
const users = [
{
name: 'John',
isActive: false,
},
{
name: 'Alice',
isActive: false,
},
{
name: 'Bob',
isActive: true,
},
];
const isOneUserActive = users.some(user => user.isActive === true);
console.log(isOneUserActive);
Executing above code will output the following:
true
Every
This method will return true if all elements passed the condition provided inside callback function otherwise it will return false.
const users = [
{
name: 'John',
isActive: false,
},
{
name: 'Alice',
isActive: true,
},
{
name: 'Bob',
isActive: true,
},
];
const isAllUserActive = users.every(user => user.isActive === true);
console.log(isAllUserActive);
Executing above code will output the following:
false
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