有没有办法直接在角度表达式中计算 json 对象中的键数？

Question

I need to show the number of keys in a json object on a web page. So, is there a way to calculate the count directly in the angular expression?

For example,

JSON:

$scope.json = {"key1": "value1", "key2": "value2", key3: "value3"}

For this 'json', there are three keys. I want to get the count of keys directly in an angular expression without calculating it in the controller.

Answer 1

You would have to use a custom filter like this:

template:

{{json | numKeys}}

filter:

app.filter('numKeys', function() {
    return function(json) {
        var keys = Object.keys(json)
        return keys.length;
    }
})

Answer 2

Some hacky way would be to do the following:

howManyKeys = {
    a: 'Do',
    b: 'I',
    c: 'have?',
}

1. If you only want to use it a few times:

This object has {{ (howManyKeys | keyValue).length }} keys
<span *ngIf="(howManyKeys | keyValue).length > 2">That's more than 2!</span>

2. If you only want to show it on many spots:

<span *ngFor="let howManyKeysLength of [(howManyKeys | keyValue).length]">
   This object has {{howManyKeysLength}} keys.
   <span *ngIf="howManyKeysLength > 2">That's more than 2!</span>
   <span *ngIf="howManyKeysLength < 5">Less than 5!</span>
</span>

This can be useful when you don't want to add a service.