AngularJS:常量与值 [英] AngularJS: Constants vs Values

问题描述

据我了解文档，常量和值之间唯一的具体区别是常量可以在应用程序配置阶段使用，而值仅在运行阶段可用.

As far as I understand the documentation, the only concrete difference between a Constant and a Value is that a Constant can be used during the apps config phase, whereas a Value is only available during the run phase.

我很好奇为什么在这种情况下需要值?它们真的只是有限的常量吗?

I am curious as to why Values are needed at all in this case? Aren't they really just limited Constants?

推荐答案

一个常量可以注入到任何地方.

一个常量不能被装饰器拦截，这意味着一个常量的值永远不应该被改变.

A constant can not be intercepted by a decorator, that means that the value of a constant should never be changed.

var app = angular.module('app', []);

app.constant('PI', 3.14159265359);

app.config(function(PI){
    var radius = 4;
    //PI can be injected here in the config block
    var perimeter = 2 * PI * radius;
});

app.controller('appCtrl', function(PI) {
    var radius = 4;
    // calculate area of the circle
    var area = PI * radius * radius; 
});

值与常量的不同之处在于值不能注入配置，但可以被装饰器拦截.

Value differs from constant in that value can not be injected into configurations, but it can be intercepted by decorators.

var app = angular.module('app', []);

app.value('greeting', 'Hello');

app.config(function ($provide) {
    $provide.decorator('greeting', function ($delegate) {
        return $delegate + ' World!';
    });
});

这篇关于AngularJS:常量与值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！