How do I set the value attribute in ng-options for AngularJS?

Setting Values in ng-options for AngularJS

AngularJS's ng-options directive allows developers to populate options for a tag. One common question that arises is how to set the value attribute for each option.

To understand the value setting mechanism, let's delve into the syntax of ngOptions. It takes an expression in one of these forms:

For arrays:

label for value in array

For objects:

label for (key, value) in object

Consider the following example array:

array = [{ "value": 1, "text": "1st" }, { "value": 2, "text": "2nd" }];

To fill the options using ng-options, we can write:

<select ng-options="obj.text as obj.value for obj in array"></select>

In this case, obj.value will determine the selected value for each option.

Update: Track by Value Expression

With recent AngularJS updates, it's now possible to explicitly specify the value for the value attribute using a track by expression:

<select ng-options="obj.text for obj in array track by obj.value"></select>

Remembering the Syntax

The ngOptions syntax can be challenging to recall. A helpful analogy is to think of it as an extended version of Python's list comprehensions:

[x**2 for x in [1, 2, 3, 4, 5]]

However, in ng-options, we distinguish between the value and the text displayed for each option using the as keyword:

person.id as person.name for person in people

For JavaScript objects, the syntax is similar, using (key, value) pairs:

for (key, value) in object

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