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Showing content from https://webplatform.github.io/docs/javascript/Array/filter below:

filter · WebPlatform Docs

filter Summary

Returns the elements of an array that meet the condition specified in a callback function.

Syntax

filter( callbackfn [, thisArg ])

callbackfn: Required. A function that accepts up to three arguments. The filter method calls the callbackfn function one time for each element in the array.
thisArg: Optional. An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.

Return Value

A new array that contains all the values for which the callback function returns true. If the callback function returns false for all elements of array1 , the length of the new array is 0.

Examples

The following example shows how to use the filter method.


 function CheckIfPrime(value, index, ar) {
     high = Math.floor(Math.sqrt(value)) + 1;

     for (var div = 2; div <= high; div++) {
         if (value % div == 0) {
             return false;
         }
     }
     return true;
 }

 
 var numbers = [31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53];

 
 var primes = numbers.filter(CheckIfPrime);

 document.write(primes);

In the following example, the callbackfn argument includes the code of the callback function.


 var arr = [5, "element", 10, "the", true];

 
 
 var result = arr.filter(
     function (value) {
         return (typeof value === 'string');
     }
 );

 document.write(result);

The following example displays the names of properties that start with the letter “css” in the window DOM object.

var filteredNames = Object.getOwnPropertyNames(window).filter(IsC);

     for (i in filteredNames)
         document.write(filteredNames[i] + "<br/>");

 
 function IsC(value) {
     var firstChar = value.substr(0, 3);
     if (firstChar.toLowerCase() == "css")
         return true;
     else
         return false;
     }

The following example illustrates the use of the thisArg argument, which specifies an object to which the this keyword can refer.

var checkNumericRange = function(value) {
     if (typeof value !== 'number')
         return false;
     else
         return value >= this.minimum && value <= this.maximum;
 }

 var numbers = [6, 12, "15", 16, "the", -12];

 
 
 var obj = { minimum: 10, maximum: 20 }

 var result = numbers.filter(checkNumericRange, obj);

 document.write(result);

The filter method can be applied to a string instead of an array. The following example shows how to do this.


 
 
 function CheckValue(value, index, ar) {
     if (index == 0)
         return true;
     else
         return ar[index - 1] === " ";
 }

 
 var sentence = "The quick brown fox jumps over the lazy dog.";

 
 var subset = [].filter.call(sentence, CheckValue);

 
 

 document.write(subset);

Remarks

The filter method calls the callbackfn function one time for each element in the array, in ascending index order. The callback function is not called for missing elements of the array.

In addition to array objects, the filter method can be used by any object that has a length property and that has numerically indexed property names.

The syntax of the callback function is as follows:

function callbackfn(value, index, array1)

You can declare the callback function by using up to three parameters.

The following table lists the callback function parameters.

Callback argument Definition value The value of the array element. index The numeric index of the array element. array1 The array object that contains the element.

The filter method does not directly modify the original array, but the callback function might modify it. The following table describes the results of modifying the array object after the filter method starts.

Condition after the filter method starts Element passed to callback function? Element is added beyond the original length of the array. No. Element is added to fill in a missing element of the array. Yes, if that index has not yet been passed to the callback function. Element is changed. Yes, if that element has not yet been passed to the callback function. Element is deleted from the array. No, unless that element has already been passed to the callback function. Exceptions

If the callbackfn argument is not a function object, a TypeError exception is thrown.

Requirements

Supported in the following document modes: Internet Explorer 9 standards, Internet Explorer 10 standards, and Internet Explorer 11 standards. Also supported in Windows Store apps. Not supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards.