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);finditemstarting from the indexfrom; -
arr.lastIndexOf(item, from)– same, but looks for from right to left. -
arr.includes(item, from)– looks foritemstarting 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.findIndexmethod 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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