Hello everyone in this article, we will know some of Javascript Array Methods
.
Before, we learned about push
, unshift
, splice
.
slice
method
slice method is used for get some elements form an array,
but not remove any item from the old array.
For example:
let arr = ["a", "b", "c", "d"];
alert( arr.slice(1, 3) ); // b,c (copy from 1 to 3)
alert( arr.slice(-2) ); // c,d (copy from -2 till the end)
negative values that get values from the end.
concat
method
The method arr.concat
creates a new array that includes values from other arrays and additional items.
arr.concat(arg1, arg2...)
For Example:
let arr = ['a', 'b'];
// create an array from: arr and ['c','d']
alert( arr.concat(['c', 'd']) ); // a,b,c,d
// create an array from: arr and ['c','d'] and ['e','f']
alert( arr.concat(['c','d'], ['e','f']) ); // a,b,c,d,e,f
// create an array from: arr and ['c','d'], then add values 'e' and 'f'
alert( arr.concat(['c','d'], 'e', 'f') ); // a,b,c,d,e,f
Iterate forEach
method
The arr.forEach
method that executes a function for every item in arr
.
The Syntax:
arr.forEach(function(item, index, array) {
// ... do something with item
});
For Example, we can alert every item in an array.
let arr = [1,2,3];
arr.forEach(function(item){
alert(item); // 1 , 2 , 3
});
You can do anything with item. For example, you can make a filter for array elements.
let arr = [1,2,3],
secondArr = [];
arr.forEach(function(item){
if(item >= 2){
secondArr.push(item);
}
});
alert(secondArr); // 2,3
Searching in array
let's cover all method that search in an array.
indexOf
, lastIndexOf
and includes
The methods arr.indexOf
, arr.lastIndexOf
and arr.includes
have the same syntax.
The Syntax:
-
arr.indexOf(item, from);
finditem
starting from the indexfrom
; -
arr.lastIndexOf(item, from)
– same, but looks for from right to left. -
arr.includes(item, from)
– looks foritem
starting from indexfrom
, returns true if found.
let arr = [1,2,3,4,5];
arr.indexOf(4, 1); // returns 3 is the index of number 4
arr.lastIndexOf(2) // returns 1 is the index of number 2
arr.includes(5) // returns true
arr.includes(10) // returns false
find
and findIndex
If we have an array and we need to find any item with the specific condition.
For Example:
we have an array like this
let arr = [
{
name: 'Ahmed',
age: 21
},
{
name: 'Mohamed',
age: 25
},
{
name: 'Mahmoud',
age: 23
}
];
and, we need to get the object have an age equal 21.
let theObject = arr.find(function(item){
return item.age === 21;
});
console.log(theObject); // {name:'Ahmed', age:21}
The
arr.findIndex
method is essentially the same, but it returns the index where the element was found instead of the element itself and -1 is returned when nothing is found.
filter
method
we use arr.filter
method to get an array from another array with specific condition.
let arr = [
{
name: 'Ahmed',
age: 21
},
{
name: 'Mohamed',
age: 25
},
{
name: 'Mahmoud',
age: 23
}
];
let newArr = arr.filter(function(item){
return item.age >= 23;
});
console.log(newArr ) // [{name:'Mahmoud', age:23}, {name:'Mohamed', age:25}];
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