在字符串中特定字符的最后一次出现之前插入

Question

如何在特定字符的最后一次出现之前插入内容？

如果 (条件成立)，则将 " again" 插入到字符串中最后一个 "<" 之前。

- Dejan Biljecki

Answer 1

你可以使用substring()和lastIndexOf()方法：

var str="Hello planet earth, you are a great planet.";
var n=str.lastIndexOf("planet");
var str2 = str.substring(0,n)+" again "+str.substring(n);
console.log(str2); // Hello planet earth, you are a great  again planet. 

作为一个很好的功能：

function insertBeforeLastOccurrence(strToSearch, strToFind, strToInsert) {
    var n = strToSearch.lastIndexOf(strToFind);
    if (n < 0) return strToSearch;
    return strToSearch.substring(0,n) + strToInsert + strToSearch.substring(n);    
}

var str ="This <br> is another <br> string <br> example.";
var newStr = insertBeforeLastOccurrence(str, "<", " again");
console.log(newStr); // This <br> is another <br> string  again<br> example.

或者作为String方法：

String.prototype.insertBeforeLastOccurrence = function(strToFind, strToInsert) {
    var n = this.lastIndexOf(strToFind);
    if (n < 0) return this.toString();
    return this.substring(0,n) + strToInsert + this.substring(n);    
}

var str ="This <br> is another <br> string <br> example.";
console.log(str.insertBeforeLastOccurrence("<", " again"));
// Output: This <br> is another <br> string  again<br> example.
console.log(str.insertBeforeLastOccurrence("w00t", " again")); // wont find
// Output: This <br> is another <br> string <br> example.

- acdcjunior

Answer 2

您可以使用lastIndexOf(str)来获取指定字符串的最后一次出现，该函数是任何String或string对象的成员函数。然后您可以像这样进行操作:

var idx = mystr.lastIndexOf("<");
if (idx > -1)
  var outval = mystr.substr(0, idx) + " again" + mystr.substr(idx);

- abiessu