在此页

• 句法
• 描述
• Polyfill
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

trimStart() method removes whitespace from the beginning of a string. trimLeft() is an alias of this method.

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.

句法

str.trimStart();
str.trimLeft();
					

返回值

A new string representing the calling string stripped of whitespace from its beginning (left end).

描述

trimStart() / trimLeft() methods return the string stripped of whitespace from its left end. trimLeft() or trimStart() do not affect the value of the string itself.

Aliasing

For consistency with functions like String.prototype.padStart the standard method name is trimStart . However, for web compatibility reasons, trimLeft remains as an alias to trimStart . In some engines this means:

String.prototype.trimLeft.name === "trimStart";
					

Polyfill

//https://github.com/FabioVergani/js-Polyfill_String-trimStart
(function(w){
    var String=w.String, Proto=String.prototype;
    (function(o,p){
        if(p in o?o[p]?false:true:true){
            var r=/^\s+/;
            o[p]=o.trimLeft||function(){
                return this.replace(r,'')
            }
        }
    })(Proto,'trimStart');
})(window);
/*
ES6:
(w=>{
    const String=w.String, Proto=String.prototype;
    ((o,p)=>{
        if(p in o?o[p]?false:true:true){
            const r=/^\s+/;
            o[p]=o.trimLeft||function(){
                return this.replace(r,'')
            }
        }
    })(Proto,'trimStart');
})(window);
*/
					

范例

使用 trimStart()

The following example displays the lowercase string 'foo  ' :

var str = '   foo  ';
console.log(str.length); // 8
str = str.trimStart();
console.log(str.length); // 5
console.log(str);        // 'foo  '
					

规范

规范
ECMAScript (ECMA-262) The definition of ' String.prototype.trimStart' in that specification.

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
trimStart	Chrome 66 66 4 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Edge 12 Alternate Name 12 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Firefox 61 61 3.5 Alternate Name Alternate Name Uses the non-standard name: trimLeft	IE No	Opera 53 53 15 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Safari 12	WebView Android 66 66 ≤37 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Chrome Android 66 66 18 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Firefox Android 61 61 4 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Opera Android 47 47 14 Alternate Name Alternate Name Uses the non-standard name: trimLeft	Safari iOS 12	Samsung Internet Android 9.0 9.0 1.0 Alternate Name Alternate Name Uses the non-standard name: trimLeft	nodejs 10.0.0 10.0.0 0.12 Alternate Name Alternate Name Uses the non-standard name: trimLeft

图例

完整支持

完整支持

不支持

不支持

使用非标名称。

另请参阅

• String.prototype.trim()
• String.prototype.trimEnd()

元数据

• 最后修改： May 20, 2020

相关话题

1. 标准内置对象
2. String
3. 特性
   1. String 长度
4. 方法
   1. String.fromCharCode()
   2. String.fromCodePoint()
   3. String.prototype.anchor()
   4. String.prototype.big()
   5. String.prototype.blink()
   6. String.prototype.bold()
   7. String.prototype.charAt()
   8. String.prototype.charCodeAt()
   9. String.prototype.codePointAt()
   10. String.prototype.concat()
   11. String.prototype.endsWith()
   12. String.prototype.fixed()
   13. String.prototype.fontcolor()
   14. String.prototype.fontsize()
   15. String.prototype.includes()
   16. String.prototype.indexOf()
   17. String.prototype.italics()
   18. String.prototype.lastIndexOf()
   19. String.prototype.link()
   20. String.prototype.localeCompare()
   21. String.prototype.match()
   22. String.prototype.matchAll()
   23. String.prototype.normalize()
   24. String.prototype.padEnd()
   25. String.prototype.padStart()
   26. String.prototype.repeat()
   27. String.prototype.replace()
   28. String.prototype.replaceAll()
   29. String.prototype.search()
   30. String.prototype.slice()
   31. String.prototype.small()
   32. String.prototype.split()
   33. String.prototype.startsWith()
   34. String.prototype.strike()
   35. String.prototype.sub()
   36. String.prototype.substr()
   37. String.prototype.substring()
   38. String.prototype.sup()
   39. String.prototype.toLocaleLowerCase()
   40. String.prototype.toLocaleUpperCase()
   41. String.prototype.toLowerCase()
   42. String.prototype.toSource()
   43. String.prototype.toString()
   44. String.prototype.toUpperCase()
   45. String.prototype.trim()
   46. String.prototype.trimEnd()
   47. String.prototype.trimStart()
   48. String.prototype.valueOf()
   49. String.prototype[@@iterator]()
   50. String.raw()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()