How to change the size and bytes of a certain bit of a string in js

There are three ways to modify the value at a specific position in a JavaScript string: use character code to get the character code of the new character, and then use it to replace the value at the specified position in the string. Use the splice() method to replace characters at specified positions in a string. For byte strings, convert the string to a Uint16Array, modify the corresponding positions, and then convert the modified Uint16Array to a string.

How to modify the value of a specific position in a JavaScript string

Method 1: Use character code

To modify the value at a specific position in a string, you can use character codes. A character code is a number that represents the corresponding value of a character in the Unicode character set.

<code class="js">const str = "Hello";
const newCharacter = "W";
const newCharCode = newCharacter.charCodeAt(0); // 获取新字符的字符代码

str[2] = String.fromCharCode(newCharCode); // 用新字符代码更改字符串中指定位置的值

console.log(str); // 输出: "Hewllo"</code>

Method 2: Use the splice() method

You can also use the splice() method to replace the characters at the specified position in the string.

<code class="js">const str = "Hello";
const replacementCharacter = "W";
const index = 2;

str.splice(index, 1, replacementCharacter); // 用新字符替换指定位置的字符

console.log(str); // 输出: "Hewllo"</code>

Modify bytes

The bytes of characters in the string cannot be modified directly, because JavaScript strings are UTF-16 encoded, and each character consists of two byte representation. To modify the bytes of a character, use the following steps:

1. Convert the string to a Uint16Array.
2. Modify the corresponding position in Uint16Array.
3. Convert the modified Uint16Array to a string.

<code class="js">const str = "Hello";
const charIndex = 2; // 修改第 3 个字符（索引从 0 开始）
const newCharacter = "W";
const charCode = newCharacter.charCodeAt(0);

// 将字符串转换成 Uint16Array
const arr = new Uint16Array(str.length);
for (let i = 0; i < str.length; i++) {
  arr[i] = str.charCodeAt(i);
}

// 修改 Uint16Array 中指定位置的值
arr[charIndex] = charCode;

// 将 Uint16Array 转换成字符串
const newStr = String.fromCharCode(...arr);

console.log(newStr); // 输出: "Hewllo"</code>

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