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.

// Arrow function
some((element) => { ... } )
some((element, index) => { ... } )
some((element, index, array) => { ... } )

// Callback function
some(callbackFn)
some(callbackFn, thisArg)

// Inline callback function
some(function callbackFn(element) { ... })
some(function callbackFn(element, index) { ... })
some(function callbackFn(element, index, array){ ... })
some(function callbackFn(element, index, array) { ... }, thisArg)

callback

A function to test for each element, taking three arguments:

element

The current element being processed in the array.

indexOptional

The index of the current element being processed in the array.

arrayOptional

The array some() was called upon.

thisArgOptional

A value to use as this when executing callbackFn.

true if the callback function returns a truthy value for at least one element in the array. Otherwise, false.

The some() method executes the callbackFn function once for each element present in the array until it finds the one where callbackFn 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. callbackFn 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.

callbackFn 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 callbackFn 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 callbackFn. Elements appended to the array after the call to some() begins will not be visited by callbackFn. If an existing, unvisited element of the array is changed by callbackFn, its value passed to the visiting callbackFn will be the value at the time that some() visits that element's index. Elements that are deleted are not visited.

some() was added to the ECMA-262 standard in the 5^th 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, 5^th 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;
  };
}

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

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

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

const fruits = ['apple', 'banana', 'mango', 'guava'];

function checkAvailability(arr, val) {
  return arr.some(arrVal => val === arrVal);
}

checkAvailability(fruits, 'kela');   // false
checkAvailability(fruits, 'banana'); // true

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

• Array.prototype.every()
• Array.prototype.forEach()
• Array.prototype.find()
• TypedArray.prototype.some()