str = str.split('');
str[3] = 'h';
str = str.join('');

使用字符串的一行程序。替换回调(不支持表情符号):

// 0 - index to replace, 'f' - replacement string
'dog'.replace(/./g, (c, i) => i == 0? 'f': c)
// "fog"

解释道:

//String.replace will call the callback on each pattern match
//in this case - each character
'dog'.replace(/./g, function (character, index) {
   if (index == 0) //we want to replace the first character
     return 'f'
   return character //leaving other characters the same
})

如果你想替换字符串中的字符，你应该创建可变字符串。这些本质上是字符数组。你可以创建一个工厂:

  function MutableString(str) {
    var result = str.split("");
    result.toString = function() {
      return this.join("");
    }
    return result;
  }

然后你可以访问字符，整个数组转换为字符串时使用的字符串:

  var x = MutableString("Hello");
  x[0] = "B"; // yes, we can alter the character
  x.push("!"); // good performance: no new string is created
  var y = "Hi, "+x; // converted to string: "Hi, Bello!"

使用扩展语法，你可以将字符串转换为数组，在给定位置分配字符，然后转换回字符串:

Const STR = "hello world"; 函数replace (s, i, c) { Const arr =[…s];//将字符串转换为数组 Arr [i] = c;//在pos i处设置字符c 返回arr.join(”);//返回字符串 ｝ //打印"hallo world" console.log(replace (str, 1， 'a'));

var str = “hello world”; console.log（str）; var arr = [...p]; arr[0] = “H”; p = arr.join（“”）; console.log（str）;

function dothis() { var x = document.getElementById("x").value; var index = document.getElementById("index").value; var text = document.getElementById("text").value; var length = document.getElementById("length").value; var arr = x.split(""); arr.splice(index, length, text); var result = arr.join(""); document.getElementById('output').innerHTML = result; console.log(result); } dothis(); <input id="x" type="text" value="White Dog" placeholder="Enter Text" /> <input id="index" type="number" min="0"value="6" style="width:50px" placeholder="index" /> <input id="length" type="number" min="0"value="1" style="width:50px" placeholder="length" /> <input id="text" type="text" value="F" placeholder="New character" /> <br> <button id="submit" onclick="dothis()">Run</button> <p id="output"></p>

此方法适用于较小长度的字符串，但对于较大的文本可能很慢。

var x = "White Dog";
var arr = x.split(""); // ["W", "h", "i", "t", "e", " ", "D", "o", "g"]
arr.splice(6, 1, 'F');

/* 
  Here 6 is starting index and 1 is no. of array elements to remove and 
  final argument 'F' is the new character to be inserted. 
*/
var result = arr.join(""); // "White Fog"