Array.prototype.some()

some() 方法會透過給定函式、測試陣列中是否至少有一個元素，通過該函式所實作的測試。這方法回傳的是布林值。

嘗試一下

備註： 如果輸入空陣列的話，這個方法會回傳 false。

語法

arr.some(callback[, thisArg])

參數

callback

用來測試每一個元素的函式，它包含三個引數：

currentValue

目前正要被處理的陣列元素。

index選擇性

目前正要被處理的陣列元素之索引值。

array選擇性

呼叫 some() 的陣列。

thisArg選擇性

執行 callback 回呼函式的 this 值。

回傳值

若回呼函式在處理任何一個陣列元素時得到 truthy (en-US) 值，則回傳 true。否則，回傳值為 false。

描述

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.

範例

測試陣列元素的數值

以下範例將測試是否最少有一個元素的數值大於 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

使用箭頭函式測試

箭頭函式能給相同的測試，提供更簡潔的語法。

[2, 5, 8, 1, 4].some(x => x > 10); //false
[12, 5, 8, 1, 4].some(x => x > 10); // true

測試陣列元素的數值是否存在

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

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 (en-US) 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: http://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;
  };
}

規範

Specification
ECMAScript Language Specification
# sec-array.prototype.some

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