javascript - typescript 生成冗余变量

Question

考虑以下 Typescript 代码:

module demoAppModule{
    'use strict';

    export module nest{
        export var hello = function () {
            alert('Hello!');
        };
    }
}

demoAppModule.nest.hello();

转译后我们有以下 javascript 代码:

var demoAppModule;
(function (demoAppModule) {
    'use strict';

    (function (nest) {
        nest.hello = function () {
            alert('Hello!');
        };
    })(demoAppModule.nest || (demoAppModule.nest = {}));
    var nest = demoAppModule.nest;
})(demoAppModule || (demoAppModule = {}));

demoAppModule.nest.hello();

为什么会产生这条线？它伤害了我的眼睛。

var nest = demoAppModule.nest;

Answer 1

简答:需要在本地访问模块变量。例如

module demoAppModule{
    'use strict';

    export module nest{
        export var hello = function () {
            alert('Hello!');
        };
    }

    // The following would not be possible without that line 
    console.log(nest.hello);
}

demoAppModule.nest.hello();

更长的答案:它类似于在模块之前添加的 var，例如注意 var x:

// TypeScript 
module x{export var foo;}
// Generated JavaScript 
var x;
(function (x) {
    x.foo;
})(x || (x = {}));

但是当你在一个模块内 + 导出一个模块时，需要将 var 添加到 outermodule.innermodule 所以你不需要做 var innermodule预先。您将它添加到 outermodule，然后创建一个局部变量以指向您可以在生成的 javascript 中看到的 innermodule:

// Notice var here 
var demoAppModule;
(function (demoAppModule) {
    'use strict';

    // Notice no var here 
    (function (nest) {
        nest.hello = function () {
            alert('Hello!');
        };
    })(demoAppModule.nest || (demoAppModule.nest = {}));
    // Notice var assinged afterwards
    var nest = demoAppModule.nest;

    // The following would not be possible without that line
    console.log(nest.hello);
})(demoAppModule || (demoAppModule = {}));

demoAppModule.nest.hello();