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  1. 給開發者的 Web 技術文件
  2. JavaScript
  3. JavaScript 參考文件
  4. 標準內建物件
  5. 字串
  6. String.prototype.padStart()
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String.prototype.padStart()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2017年4月.

實驗性質: 這是一個實驗中的功能
此功能在某些瀏覽器尚在開發中，請參考兼容表格以得到不同瀏覽器用的前輟。

padStart() 會將用給定用於填充的字串，以重複的方式，插入到目標字串的起頭(左側)，直到目標字串到達指定長度。

In this article

Syntax

js
str.padStart(targetLength [, padString])

Parameters

targetLength

目標字串被填充後的長度。如果此參數小於原字串的長度，那將直接返回原字串。

padString 選擇性

用來填充的字串。如果填充字串太長，則由左側開始，擷取所需要的長度。此參數預設值是空白 " " (U+0020).

Return value

目標字串被填充到指定長度後，所得的新字串。

Examples

js
"abc".padStart(10); // " abc" "abc".padStart(10, "foo"); // "foofoofabc" "abc".padStart(6, "123465"); // "123abc"

規範

Specification
ECMAScript® 2027 Language Specification
# sec-string.prototype.padstart

瀏覽器相容性

Enable JavaScript to view this browser compatibility table.

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  1. 標準內建物件
  2. String
  3. 建構子
    1. String()
  4. 靜態方法
    1. fromCharCode()
    2. fromCodePoint()
    3. raw()
  5. 實體方法
    1. anchor()
    2. at()
    3. big()
    4. blink()
    5. bold()
    6. charAt()
    7. charCodeAt()
    8. codePointAt()
    9. String.prototype.concat()
    10. endsWith()
    11. fixed()
    12. fontcolor()
    13. fontsize()
    14. includes()
    15. indexOf()
    16. isWellFormed()
    17. italics()
    18. lastIndexOf()
    19. link()
    20. String.prototype.localeCompare()
    21. match()
    22. matchAll()
    23. normalize()
    24. padEnd()
    25. String.prototype.padStart()
    26. repeat()
    27. replace()
    28. replaceAll()
    29. search()
    30. slice()
    31. small()
    32. split()
    33. startsWith()
    34. strike()
    35. sub()
    36. substr()
    37. substring()
    38. sup()
    39. toLocaleLowerCase()
    40. toLocaleUpperCase()
    41. String.prototype.toLowerCase()
    42. toString()
    43. toUpperCase()
    44. toWellFormed()
    45. String.prototype.trim()
    46. trimEnd()
    47. trimStart()
    48. valueOf()
    49. [Symbol.iterator]()
  6. 實體屬性
    1. length
  7. 繼承
  8. Object/Function
  9. 靜態方法
    1. Function.prototype.apply()
    2. Function.prototype.bind()
    3. Function.prototype.call
    4. toString()
    5. [Symbol.hasInstance]()
  10. 靜態屬性
    1. displayName
    2. Function.length
    3. name
    4. prototype
    5. arguments
    6. caller
  11. 實體方法
    1. __defineGetter__()
    2. __defineSetter__()
    3. __lookupGetter__()
    4. __lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. isPrototypeOf()
    7. propertyIsEnumerable()
    8. toLocaleString()
    9. toString()
    10. valueOf()
  12. 實體屬性
    1. __proto__
    2. constructor

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