ES6生成器的Function.prototype.apply的等價物

Question

我試圖構建一個可鏈接的JavaScript API。 （我在V8的最新版本中啓用了迭代器和生成器。）在下面的例子中，setState是可鏈接的。它也允許你調用它，而不必明確地創建一個新的實例Builder。 chain()幫助函數處理該函數並自動返回該實例，因此setState不必擔心它。 （贏得一流功能！）

除了可鏈式方法，我想要一些「終止」方法。踢球者是這些「終結者」是發電機。發生器產生一個Builder實例的內部狀態。問題是我找不到一個相當於f.apply(that, arguments)的發電機。我希望能夠在運行時調用生成器並設置其this上下文，就像您可以使用Function.prototype.apply和Function.prototype.call一樣。

的變通，評論與Yuck!，是揭露雙方的委託和在Builder.prototype原來的發電機，呼籲從委派原。有沒有辦法像chain方法一樣實現等效包裝，而不必暴露Builder.prototype上的_generate方法？

function Builder() { this.initialState = 'initialState'; }; 
Builder.prototype.setState = chain(function(k, v) { this[k] = v; }); 
Builder.prototype.generate = delegate(generate, '_generate'); // Yuck! 
Builder.prototype._generate = generate; 


function chain(f) { 
    return function() { 
    var that = (this instanceof Builder) ? this : new Builder(); 
    f.apply(that, arguments); // Pass through arguments 
    return that; 
    } 
} 

function delegate(gen, _gen) { 
    return function*() { 
    var that = (this instanceof Builder) ? this : new Builder(); 
    that.setState('delegated', true);    
    yield *that[_gen](); // Yuck! 
    } 
} 

function *generate(opts) { 
    var i = 0; 
    for(var i = 0; i < 10; i++) { 
    yield [Object.keys(this), opts, i].join(','); 
    } 
} 

// Set up a namespace 
var ns = {}; 
ns.setState = Builder.prototype.setState; 
ns.generate = Builder.prototype.generate; 


var itr = ns 
// .setState('a', 'A') 
// .setState('b', 'B') 
// .setState('c', 'C') 
    .generate('options'); 


var out = []; 
for(var value of itr) { out.push(value); } 
out; 

它返回

[ 
    "initialState,delegated,,0", 
    "initialState,delegated,,1", 
    "initialState,delegated,,2", 
    "initialState,delegated,,3", 
    "initialState,delegated,,4", 
    "initialState,delegated,,5", 
    "initialState,delegated,,6", 
    "initialState,delegated,,7", 
    "initialState,delegated,,8", 
    "initialState,delegated,,9" 
] 

Answer 1

的關鍵是在匿名發電機外殼yield *gen.apply(that, arguments)。

function Builder() { this.initialState = 'initialState'; }; 
Builder.prototype.setState = chain(function(k, v) { this[k] = v; }); 
Builder.prototype.generate = delegate(generate); 

// Reuses or creates a Builder instance and makes it `this` for calling `f`. 
// Returns the Builder instance. 
function chain(f) { 
    return function() { 
    var that = (this instanceof Builder) ? this : new Builder(); 
    f.apply(that, arguments); // Pass through arguments 
    return that; 
    } 
} 

// Similar to `chain()` to create a Builder instance if it doesn't exist. 
// Generators are terminal, though, so this returns the FunctionGenerator. 
function delegate(gen) { 
    return function*() { 
    var that = (this instanceof Builder) ? this : new Builder(); 
    that.setState('delegated', true);    
    yield *gen.apply(that, arguments); 
    } 
} 

function *generate(opts) { 
    var i = 0; 
    for(var i = 0; i < 10; i++) { 
    yield [Object.keys(this), opts, i].join(','); 
    } 
} 

// Set up a namespace 
var ns = {}; 
ns.setState = Builder.prototype.setState; 
ns.generate = Builder.prototype.generate; 


var itr = ns 
// .setState('a', 'A') 
// .setState('b', 'B') 
// .setState('c', 'C') 
    .generate('options'); 


var out = []; 
for(var value of itr) { out.push(value); } 
out; 

Answer 2

的問題是，我無法弄清楚一個相當於f.apply（即，參數）的發電機。

從ES6 draft來判斷，你不需要等價的 - 你可以直接使用表達式。生成器函數（構造生成器實例）是函數，它們繼承（通過Generator.prototype）從Function.prototype;您可以像使用其他功能一樣使用.call和.apply。

所以下面應該工作：

function delegate(gen) { 
    return function() { 
    var that = (this instanceof Builder) ? this : new Builder(); 
    that.setState('delegated', true);    
    return gen.apply(that, arguments); // Pass through arguments 
    } 
}