Array.prototype.some()
The some()
method tests whether
at least one element in the array passes the test implemented by the provided
function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Syntax
arr.some(callback(element[, index[, array]])[, thisArg])
Parameters
callback
-
A function to test for each element, taking three arguments:
element
- The current element being processed in the array.
index
Optional- The index of the current element being processed in the array.
array
Optional- The array
some()
was called upon.
thisArg
Optional- A value to use as
this
when executingcallback
.
Return value
true
if the callback function returns a truthy value for
at least one element in the array. Otherwise, false
.
Description
The some()
method executes the callback
function
once for each element present in the array until it finds the one where
callback
returns a truthy value (a value that becomes
true when converted to a Boolean). If such an element is found, some()
immediately returns true
. Otherwise, some()
returns
false
. callback
is invoked only for indexes of the
array with assigned values. It is not invoked for indexes which have been deleted or
which have never been assigned values.
callback
is invoked with three arguments: the value of the
element, the index of the element, and the Array object being traversed.
If a thisArg
parameter is provided to some()
, it
will be used as the callback's this
value. Otherwise, the value
undefined
will be used as its this
value. The
this
value ultimately observable by callback
is
determined according to the usual rules for
determining the this
seen by a function.
some()
does not mutate the array on which it is called.
The range of elements processed by some()
is set before the first
invocation of callback
. Elements appended to the array after the
call to some()
begins will not be visited by
callback
. If an existing, unvisited element of the array is
changed by callback
, its value passed to the visiting
callback
will be the value at the time that some()
visits that element's index. Elements that are deleted are not visited.
Caution: Calling this method on an empty array returns
false
for any condition!
Polyfill
some()
was added to the ECMA-262 standard in the 5th edition,
and it may not be present in all implementations of the standard. You can work around
this by inserting the following code at the beginning of your scripts, allowing use of
some()
in implementations which do not natively support it.
This algorithm is exactly the one specified in ECMA-262, 5th edition,
assuming Object
and TypeError
have their original values and
that fun.call
evaluates to the original value of
Function.prototype.call()
.
// Production steps of ECMA-262, Edition 5, 15.4.4.17
// Reference: https://es5.github.io/#x15.4.4.17
if (!Array.prototype.some) {
Array.prototype.some = function(fun, thisArg) {
'use strict';
if (this == null) {
throw new TypeError('Array.prototype.some called on null or undefined');
}
if (typeof fun !== 'function') {
throw new TypeError();
}
var t = Object(this);
var len = t.length >>> 0;
for (var i = 0; i < len; i++) {
if (i in t && fun.call(thisArg, t[i], i, t)) {
return true;
}
}
return false;
};
}
Examples
Testing value of array elements
The following example tests whether any element in the array is bigger than 10.
function isBiggerThan10(element, index, array) {
return element > 10;
}
[2, 5, 8, 1, 4].some(isBiggerThan10); // false
[12, 5, 8, 1, 4].some(isBiggerThan10); // true
Testing array elements using arrow functions
Arrow functions provide a shorter syntax for the same test.
[2, 5, 8, 1, 4].some(x => x > 10); // false
[12, 5, 8, 1, 4].some(x => x > 10); // true
Checking whether a value exists in an array
To mimic the function of the includes()
method, this custom
function returns true
if the element exists in the array:
const fruits = ['apple', 'banana', 'mango', 'guava'];
function checkAvailability(arr, val) {
return arr.some(function(arrVal) {
return val === arrVal;
});
}
checkAvailability(fruits, 'kela'); // false
checkAvailability(fruits, 'banana'); // true
Checking whether a value exists using an arrow function
const fruits = ['apple', 'banana', 'mango', 'guava'];
function checkAvailability(arr, val) {
return arr.some(arrVal => val === arrVal);
}
checkAvailability(fruits, 'kela'); // false
checkAvailability(fruits, 'banana'); // true
Converting any value to Boolean
const TRUTHY_VALUES = [true, 'true', 1];
function getBoolean(value) {
'use strict';
if (typeof value === 'string') {
value = value.toLowerCase().trim();
}
return TRUTHY_VALUES.some(function(t) {
return t === value;
});
}
getBoolean(false); // false
getBoolean('false'); // false
getBoolean(1); // true
getBoolean('true'); // true
Specifications
Browser compatibility
BCD tables only load in the browser