Iterating over basic “for” loop using Handlebars.js

Question

I’m new to Handlebars.js and just started using it. Most of the examples are based on iterating over an object. I wanted to know how to use handlebars in basic for loop.

Example.

for(i=0 ; i<100 ; i++) {
   create li's with i as the value
}

How can this be achieved?

score 193 · Accepted Answer · answered Aug 12 '12 at 19:06

193

There's nothing in Handlebars for this but you can add your own helpers easily enough.

If you just wanted to do something n times then:

Handlebars.registerHelper('times', function(n, block) {
    var accum = '';
    for(var i = 0; i < n; ++i)
        accum += block.fn(i);
    return accum;
});

and

{{#times 10}}
    <span>{{this}}</span>
{{/times}}

If you wanted a whole for(;;) loop, then something like this:

Handlebars.registerHelper('for', function(from, to, incr, block) {
    var accum = '';
    for(var i = from; i < to; i += incr)
        accum += block.fn(i);
    return accum;
});

and

{{#for 0 10 2}}
    <span>{{this}}</span>
{{/for}}

Demo: http://jsfiddle.net/ambiguous/WNbrL/

answered Aug 12 '12 at 19:06

mu is too short

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+1 for the helpers. As a side note, nesting the for helper won't work in scenarios where you need to refer back to the initial data. i.e data: { rows : 12, cols: 3}. – backdesk Mar 19 '14 at 15:55
1

When printing `{{../this}}` inside a nested `{{#times}}` block I've noticed that sometimes it will be `[Object object]` instead of the actual numer (one time per nested loop). – dude Mar 23 '18 at 10:05
@dude Do you have a runnable example of that? I haven't touched Handlebars for a couple years. – mu is too short Mar 23 '18 at 17:23
Inside the loop, I cannot retrieve data from handlebar, do you guys have any ideas about it? – HungDQ Apr 08 '19 at 02:06
@HungDQ Sorry but I don't know what you're trying to do, try asking a new question with all the necessary details. – mu is too short Apr 08 '19 at 02:48
@muistooshort I've created a new question with necessary details: https://stackoverflow.com/questions/55567260/handlebars-js-iterating-over-for-loop-using-handle-without-losing-data Thank you very much! – HungDQ Apr 08 '19 at 06:18
I'm getting `expected the second argument to be a number` error – Mahmoud Heretani Jan 19 '20 at 20:17
@MahmoudHeretani You're getting that error from what? Which line? – mu is too short Jan 19 '20 at 20:29
from the helper function line {{#times 10}} @muistooshort – Mahmoud Heretani Jan 19 '20 at 20:33
@MahmoudHeretani Which line of the helper? Can you reproduce the error at jsfiddle.net? – mu is too short Jan 19 '20 at 20:50
Is there a way to get the index of the loop? For example `{{this}}` – Longblog Mar 09 '22 at 22:28
1

@Longblog Sorry, haven't used Handlebars in years so I'm not sure. You could compute the index yourself given `this` and the loop's `from` and `incr` or perhaps call the `block.fn` with an object containing whatever you need. – mu is too short Mar 10 '22 at 01:52

score 26 · Answer 2 · edited Mar 21 '17 at 10:09

26

Top answer here is good, if you want to use last / first / index though you could use the following

Handlebars.registerHelper('times', function(n, block) {
    var accum = '';
    for(var i = 0; i < n; ++i) {
        block.data.index = i;
        block.data.first = i === 0;
        block.data.last = i === (n - 1);
        accum += block.fn(this);
    }
    return accum;
});

and

{{#times 10}}
    <span> {{@first}} {{@index}} {{@last}}</span>
{{/times}}

edited Mar 21 '17 at 10:09

Kannan J

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answered Jan 04 '17 at 12:00

Mike Mellor

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This helper seems to not allow to use @../index or @../last when coming to nested uses of the Helper. Is this right or maybe I did something wrong? – madtyn Jun 13 '17 at 10:43

score 9 · Answer 3 · answered Jan 25 '14 at 08:14

9

If you like CoffeeScript

Handlebars.registerHelper "times", (n, block) ->
  (block.fn(i) for i in [0...n]).join("")

and

{{#times 10}}
  <span>{{this}}</span>
{{/times}}

answered Jan 25 '14 at 08:14

Manuel

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score 9 · Answer 4 · answered Sep 03 '15 at 21:45

This snippet will take care of else block in case n comes as dynamic value, and provide @index optional context variable, it will keep the outer context of the execution as well.

/*
* Repeat given markup with given times
* provides @index for the repeated iteraction
*/
Handlebars.registerHelper("repeat", function (times, opts) {
    var out = "";
    var i;
    var data = {};

    if ( times ) {
        for ( i = 0; i < times; i += 1 ) {
            data.index = i;
            out += opts.fn(this, {
                data: data
            });
        }
    } else {

        out = opts.inverse(this);
    }

    return out;
});

I like this approach better because you have the @index variable at hand. Also you can easily add other variables depending on specific needs. — ChrisRich, Jan 29 '16 at 10:15

score 8 · Answer 5 · edited Nov 24 '20 at 14:25

8

Couple of years late, but there's now each available in Handlebars which allows you to iterate pretty easily over an array of items.

https://handlebarsjs.com/guide/builtin-helpers.html#each

edited Nov 24 '20 at 14:25

Dharman

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answered Nov 24 '20 at 14:19

Sebastijan Dumančić

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Iterating over basic “for” loop using Handlebars.js

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