str.replace（），获取匹配数或替代的最后一个元素？

Question

I have a string that uses placeholders that I'm trying to substitute with the result of function.To give an idea:

sometext = "%number% text text %number%"replace(/%\w+%/g, function(parm) {
       return 'customtext';
}

What I would like to know is there a way to get the number of matches? I need that number so I can check if the current running function is substituting the last element, and if so, return something else.Something like this in the body of function

if(lastElement) {
   return 'something else';
}

sometext = "%number% text text %number%"replace(/%\w+%/g, function(parm) {
       return 'customtext';

Answer 1

You can't directly get the number of matches in the function. It's not provided.

I'd simply count it before and count the function calls during the replacement :

var i = 0, n = str.split(/%\w+%/).length-1;
var sometext = str.replace(/%\w+%/g, function() {
   if (++i==n) return 'last text';
   else return 'not last text';
});

Answer 2

I think you want to use javascript's .match() function. You give it a regular expression, and it returns an array of matches. You can then get the length of the array.

See:

http://www.w3schools.com/jsref/jsref_match.asp

Answer 3

This will give the number of matches:

var last = "%number% text text %number%".match(/%\w+%/g).length;

Then put your 'if' in the callback that you are using and keep track with a counter of how many times the callback has been executed comparing to the length gleaned above and voila.

Cheers.

Answer 4

First, find the number of matches:

var matchCount = haystack.match(needle);

Then, count down the number of remaining matches on each replace:

haystack.replace(needle, function(param) {
    matchCount--;
    if( matchCount == 0 ) {
        return 'Last Element';
    }
    return 'Not Last Element';
});

The combined code would look something like this:

var haystack = "%number% text text %number%";
var needle = new RegExp("%\w+%", "g");

var matchCount = haystack.match(needle);
haystack.replace(needle, function(param) {
    matchCount--;
    if( matchCount == 0 ) {
        return 'Last Element';
    }
    return 'Not Last Element';
});

And can be shortened to a function similar to this:

function customReplace(haystack, needle) {
    var count = haystack.match(needle);
    haystack.replace(needle, function() {
        return (--count ? 'notLast' : 'isLast');
    });
}