是否可以在 Javascript 中使用方法链分配字符串？

Question

I want to use method chaining syntax using JavaScript and AngularJS. I assign arrays and strings.

This code works:

$mdDateLocaleProvider
     .shortDays = ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá']
     .msgCalendar = 'Calendario'
;

This code doesn't work:

$mdDateLocaleProvider
     .shortDays = ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá']
     .msgCalendar = 'Calendario'
     .msgOpenCalendar = 'Abrir calendario'
;

I think the msgOpenCalendar = 'Abrir calendario' sentence is failing due to the string assignment.

My solution:

$mdDateLocaleProvider
     .shortDays = ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá']
     .msgCalendar = 'Calendario'
;
$mdDateLocaleProvider
     .msgOpenCalendar = 'Abrir calendario'
;

Why is there a problem assigning a string but isn't with an array?

Answer 1

The name is method chaining for a reason, it is used to chain methods , not variable assignments.

In method chaining, you are simply returning the object instance (of a mutable or a new immutable object) in the end of the method (function), so you can call the next function "right away".

The reason it "works" is that an array in JS is an object, so you simply placed a msgCalendar property on the array that you assigned to shortDays property.

Basically, what you achieved is:

var shortDays = ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá'].msgCalendar = 'Calendario';
// here shortDays actually equals to 'Calendario', because it is like writing a = b = 2.
$mdDateLocaleProvider.shortDays = shortDays;
$mdDateLocaleProvider.msgOpenCalendar = 'Abrir calendario';

Answer 2

You cannot use method chaining with direct assignments like you're doing. As explained by Ron, what you think it does is not what it's actually doing.

A way of working around this is implementing the Builder pattern that would allow you to create objects based on chaining their setters methods.

Answer 3

You cannot use chaining, but as you included the angularjs tag in the question, you probably want to look at using angular.extend :

angular.extend($mdDateLocaleProvider, {
     shortDays: ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá'],
     msgCalendar: 'Calendario',
     msgOpenCalendar: 'Abrir calendario'
});

which will have the desired effect of updating the three properties and you can even use method chaining on the result if you want to call any methods.

Answer 4

You want assign() .

 Object.assign($mdDateLocaleProvider, {
      shortDays : ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá']
      msgCalendar : 'Calendario'
      msgOpenCalendar : 'Abrir calendario'
 });

Which will set everything at once for you.

---

If you need to actually chain say like maybe set shortDays , call a function, then set msgCalendar , try my shim.
This will also work for when assign doesnt work (setting DOM onclick s or innerText s), or you need to call a function that doesn't chain.

 wrap($mdDateLocaleProvider)
      .set('shortDays'      , ['Do', 'Lu', 'Ma', 'Mi', 'Ju', 'Vi', 'Sá'])
      .set('msgCalendar'    , 'Calendario')
      .set('msgOpenCalendar', 'Abrir calendario')
 ;

Simply call wrap() and away you go.

wrap = (obj) => (Object.defineProperty(obj,
            'define', {value:(name, options) => (Object.defineProperty(obj, name, options))})
    .define('assign', {value:(props)         => (Object.assign(obj, props))                })
    .define('set'   , {value:(name, value)   => { obj[name] = value; return obj; }         })
    .define('invoke', {value:(name, ...args) => { obj[name](...args); return obj; }        })
);

Demo

let bob = {
    hello  : 'there',
    chains : () => {bob.I_RAN = true; return bob;},
    doesnt : (arg1, arg2) => {bob.I_RAN_ALSO = [arg1, arg2]; return null;}
};
wrap(bob)
    .set('oh', 'my')
    .chains()
    .invoke('doesnt', 'works', 'anyway')
    .assign({more:7, stuff:null})
;
for (let item of Object.keys(bob))
      console.log(`'${item}' : ${bob[item]}`);

Output: