String.prototype.toUpperCase()

toUpperCase()  方法返回一个将调用字符串转换为大写形式的值。(如果这个值不是字符串则会被变成字符串)

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语法

str.toUpperCase()

返回值

一个表示调用字串转换成大写格式的新字符串。

异议

TypeError
When called on null or undefined, for example, String.prototype.toUpperCase.call(undefined).

描述

toUpperCase 将调用该方法的字符串值转换为大写形式,并返回。toUpperCase 方法不影响字符串本身的值因为JavaScript的strings是immutable的(不可改变的)。

示例

例子:使用 toUpperCase

​console.log( "alphabet".toUpperCase() ); // "ALPHABET"

将非字符串形式的 this 值转换成字符串

这个方法会将任何非字符串形式的值转换成字符串, 当你把这个值的 this 设置成一个不是字符串的值时:

const a = String.prototype.toUpperCase.call({
  toString: function toString() {
    return 'abcdef';
  }
});

const b = String.prototype.toUpperCase.call(true);

// prints out 'ABCDEF TRUE'.
console.log(a, b);

规范

Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262)
String.prototype.toUpperCase
Standard
ECMAScript 2015 (6th Edition, ECMA-262)
String.prototype.toUpperCase
Standard

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相关链接