Iterative Methods in Javascript array

Description

Javascript array has five iterative methods.

• every() - Runs a function on every item and returns true if the function returns true for every item.
• filter() - Runs a function on every item and returns an array of all items for which the function returns true.
• forEach() - Runs a function on every item . No return value.
• map() - Runs a function on every item and returns the result in an array.
• some() - Runs a function on every item and returns true if the function returns true for any one item.

Each of the methods accepts two arguments:

• a function to run
• an optional scope object in which to run the function changing the value of this.

The function passed into will receive three arguments:

• the array item value,
• the position of the item in the array, and
• the array object itself.

These methods do not change the values contained in the array.

Example

var numbers = [1,2,3,4,5,4,3,2,1];
//  ww  w  .ja  v  a 2s.  co m
var everyResult = numbers.every(function(item, index, array){
    return (item > 2);
});
console.log(everyResult);       //false

var someResult = numbers.some(function(item, index, array){
    return (item > 2);
});
console.log(someResult);       //true

var filterResult = numbers.filter(function(item, index, array){
    return (item > 2);
 });

console.log(filterResult);   //[3,4,5,4,3]

var mapResult = numbers.map(function(item, index, array){
    return item * 2;
 });

console.log(mapResult);   //[2,4,6,8,10,8,6,4,2]

numbers.forEach(function(item, index, array){
    console.log(item);
    console.log(index);
});

The code above generates the following result.