String.prototype导致循环提前退出

Question

I have defined a method of String.prototype called clean

String.prototype.clean = function() {       
        clean = new Array();
        tokens = [
            ['&', '&'],
            ['"', '"'],
            ["'", '''],
            ['<', '&lt;'],
            ['>', '&gt;']
        ];
        for(i = 0; i < this.length; i++) {      
            s = this[i];

            for(a = 0; a < tokens.length; a++) {
                if(tokens[a][0] == s) {
                    s = tokens[a][1];
                    break;
                }
            }

            clean.push(s);          

        }

        str =  clean.join("");
        return str;
    }

It seems to work when called in a loop, like this:

str = ["<script>", "<", ">"];
    for(i = 0; i < 3; i++) {
        console.log(str[i].clean());
    }

The for loop breaks after the first call to clean() and the console looks like this:

[2/20/2014 8:19:26 PM] <script> 

Why is this happening, and what am I doing wrong here?

Output excepted:

<script>
<
>

Answer 1

Here is a very fast way to do the same:

var __entityMap = {
    "&": "&",
    "<": "&lt;",
    ">": "&gt;",
    '"': '&quot;',
    "'": '&#39;',
    "/": '&#x2F;'
};

String.prototype.toHtml = function() {
    return String(this).replace(/[&<>"'\/]/g, function (s) {  
        return __entityMap[s];
    });
}

I have yet to find a quicker way....

Answer 2

You have:

str = ["<script>", "<", ">"];
for(i = 0; i < 3; i++) {
    console.log(str[i].clean());
}

which creates a global variable i when executed. You then have:

String.prototype.clean = function() {     
    ...
    for(i = 0; i < this.length; i++) {      
    ...
}

which modifies the value of the global i . Always keep variables in an appropriate context by declaring with var , eg:

for (var i = 0; ...; ...) {