Javascript – conditional on last item in array using handlebars.js template

arrayshandlebars.jshelpersjavascripttemplating

I am leveraging handlebars.js for my templating engine and am looking to make a conditional segment display only if it is the last item in array contained in the templates configuration object.

{
  columns: [{<obj>},{<obj>},{<obj>},{<obj>},{<obj>}]
}

I've already pulled in a helper to do some equality/greater/less-than comparisons and have had success identifying the initial item this way but have had no luck accessing my target array's length.

Handlebars.registerHelper('compare', function(lvalue, rvalue, options) {...})

"{{#each_with_index columns}}"+
"<div class='{{#equal index 0}} first{{/equal}}{{#equal index ../columns.length()}} last{{/equal}}'>"+
"</div>"+
"{{/each_with_index}}"

Does anyone know a shortcut, different approach, and some handlebars goodness that will keep me from having to tear into the handlebars.js engine to determine best course?

Best Answer

Since Handlebars 1.1.0, first and last has become native to the each helper. See ticket #483.

The usage is like Eberanov's helper class:

{{#each foo}}
    <div class='{{#if @first}}first{{/if}}{{#if @last}} last{{/if}}'>{{@key}} - {{@index}}</div>
{{/each}}

Related Solutions

Javascript – Why is using “for…in” for array iteration a bad idea

The reason is that one construct:

var a = []; // Create a new empty array.
a[5] = 5;   // Perfectly legal JavaScript that resizes the array.

for (var i = 0; i < a.length; i++) {
    // Iterate over numeric indexes from 0 to 5, as everyone expects.
    console.log(a[i]);
}

/* Will display:
   undefined
   undefined
   undefined
   undefined
   undefined
   5
*/

can sometimes be totally different from the other:

var a = [];
a[5] = 5;
for (var x in a) {
    // Shows only the explicitly set index of "5", and ignores 0-4
    console.log(x);
}

/* Will display:
   5
*/

Also consider that JavaScript libraries might do things like this, which will affect any array you create:

// Somewhere deep in your JavaScript library...
Array.prototype.foo = 1;

// Now you have no idea what the below code will do.
var a = [1, 2, 3, 4, 5];
for (var x in a){
    // Now foo is a part of EVERY array and 
    // will show up here as a value of 'x'.
    console.log(x);
}

/* Will display:
   0
   1
   2
   3
   4
   foo
*/

Javascript – How to insert an item into an array at a specific index (JavaScript)

You want the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).

In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,Borge

Best Answer

Related Solutions

Javascript – Why is using “for…in” for array iteration a bad idea

Javascript – How to insert an item into an array at a specific index (JavaScript)

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