find ids with a specific string

Question

I'm trying to learn JavaScript, and I wanted to change what I am working on into a pure JavaScript solution. How do I change this to JavaScript:

var hrefs = $("a[id^=a_l_]").map(function() {
  return this.href;
}).get();

It basically finds all id's containing "a_l_" and puts it into an array.

Here is what I have tried

var matches = [];
var elems = document.getElementsByTagName("a");
for (var i=0; i<elems.length; i++) {
  if (elems[i].id.indexOf("a_l_") == 0)
  matches.push(elems[i]);
  console.log(matches);
}

on the face of it that code looks OK - what's actually happening with it? — Alnitak
– Alnitak, Commented May 31, 2012 at 10:04

powtac · Accepted Answer · 2012-05-31 09:58:10Z

2

Always use brackets {} for conditions! Else soon or later you will make mistakes!

for (var i=0; i<elems.length; i++) {
    if (elems[i].id.indexOf("a_l_") == 0) { // <-- {
        matches.push(elems[i]);
        console.log(matches);
    }                                       // <-- }
}

answered May 31, 2012 at 9:58

powtac

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Comments

xdazz · Accepted Answer · 2012-05-31 10:11:11Z

0

You could first do a filter, then do a map.

var hrefs = Array.prototype.filter.call(document.getElementsByTagName("a"), function(node) { 
  return node.id.indexOf("a_l_") === 0;
}).map(function(node) {
  return node.href;
});

edited May 31, 2012 at 10:11

answered May 31, 2012 at 10:05

xdazz

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Comments

Someth Victory · Accepted Answer · 2012-05-31 10:10:16Z

0

You are trying to find all elements with id equal "a_l_" and add them to an array. I suggest you shouldn't have the same id for your html elements. You should move them to class. Anyway, try this:

var matches = [];
var elems = document.getElementsByTagName("a");
for(var i=0; i<elems.length; i++) {
  if(elems[i].id.indexOf("a_l_") != -1) {
    matches.push(elems[i]);
    console.log(matches);
  }
}

answered May 31, 2012 at 10:10

Someth Victory

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Comments

Alnitak · Accepted Answer · 2012-05-31 10:13:01Z

0

Assuming ES5 array methods (use a shim / polyfill if they don't exist)

var hrefs = [].filter.call(document.getElementsByTagName('a'), function(el) {
    return el.id.indexOf('a_l_') === 0;
}).map(function(el) {
    return el.href;
});

working demo at http://jsfiddle.net/alnitak/Zu3dJ/

answered May 31, 2012 at 10:13

Alnitak

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Comments

Fabrizio Calderan · Accepted Answer · 2012-05-31 10:16:48Z

0

An alternative solution in pure Javascript, working on modern browser (IE8+ included)

var elems = document.querySelectorAll("a[id^='a_l_']");

elems is a collection of <a> elements whose id are starting with a_l_. Indeed querySelectorAll is slower but readability is hugely increased

answered May 31, 2012 at 10:16

Fabrizio Calderan

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