js字符串替换

在JavaScript中，字符串是不可变的

需要自己定义replaceAt()

String.prototype.replaceAt=function(index, replacement) {
    return this.substr(0, index) + replacement+ this.substr(index + replacement.length);
}

var hello="Hello World";
alert(hello.replaceAt(2, "!!")); //should display He!!o World

const replaceStr1 = (str, index, char) => {
    const strAry = str.split('');
    strAry[index] = char;
    return strAry.join('');
  }
  replaceStr(str1, 4, '-'); // => Good-Morning
  replaceStr(str2, 4, '-'); // => Hell- World

js字符转数组

// 第一种 split拆分 "abc".split('') ==> ["a","b","c"] 
// 第二种 [...] [..."abc"] ==> ["a","b","c"] Array.from("abc") ==> ["a","b","c"]

lines[i].split('')；

js 截取前后字符

前

//前
publicstaticvoidsubstringTest01(){
    String str = "http_https://www.baidu.com/";
    //截取_之前字符串
    String str1 = str.substring(0, str.indexOf("_"));
    System.out.println("截取_之前字符串:"+str1);
}

后