JavaScript String substring()用法及代碼示例

const message = "JavaScript is fun.";

// get the substring starting from index 0 to 10
let result = message.substring(0, 10);
console.log(result);

// Output: JavaScript

substring() 語法

用法:

str.substring(indexStart, indexEnd)

在這裏，str 是一個字符串。

參數：

substring() 方法包含：

• indexStart - 開始包含在返回的子字符串中的第一個字符的索引。
• indexEnd(可選)- 停止提取的索引。 (獨占)如果省略，則提取到字符串的末尾。

返回：

• 返回包含給定字符串的指定部分的新字符串。

注意：substring()不改變原始字符串。

示例 1：使用子字符串

let string = "Programiz JavaScript Tutorials";

// first character
substr1 = string.substring(0, 1);
console.log(substr1); // P

// if start > end, they are swapped
substr2 = string.substring(1, 0);
console.log(substr2); // P

// From 11th to last character
substr3 = string.substring(10);
console.log(substr3); // JavaScript Tutorials

// the extreme values are 0 and str.length

// same as string.substring(0)
substr4 = string.substring(-44, 90);
console.log(substr4); // Programiz JavaScript Tutorials

// indexEnd is exclusive
substr5 = string.substring(0, string.length - 1);
console.log(substr5); // Programiz JavaScript Tutorial

輸出

P
P
JavaScript Tutorials
Programiz JavaScript Tutorials
Programiz JavaScript Tutorial

示例 2：替換字符串中的子字符串

// Replaces old characters with new characters in a string
function replaceString(oldChars, newChars, string) {
  for (let i = 0; i < string.length; ++i) {
    if (string.substring(i, i + oldChars.length) == oldChars) {
      string =
        string.substring(0, i) +
        newChars +
        string.substring(i + oldChars.length, string.length);
    }
  }
  return string;
}

const string = "Java Tutorials";
let newString = replaceString("Java", "JavaScript", string);
console.log(newString); // JavaScript Tutorials

輸出

JavaScript Tutorials