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The GeneratorFunction
constructor creates a new generator function
object. In JavaScript every generator function is actually a GeneratorFunction
object.
Note that GeneratorFunction
is not a global object. It could be obtained by evaluating the following code.
Object.getPrototypeOf(function*(){}).constructor
Syntax
new GeneratorFunction ([arg1[, arg2[, ...argN]],] functionBody)
Parameters
arg1, arg2, ... argN
- Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "
x
", "theValue
", or "a,b
". functionBody
- A string containing the JavaScript statements comprising the function definition.
Description
generator function
objects created with the GeneratorFunction
constructor are parsed when the function is created. This is less efficient than declaring a generator function with a function* expression
and calling it within your code, because such functions are parsed with the rest of the code.
All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.
Note: generator function
created with the GeneratorFunction
constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the GeneratorFunction
constructor was called. This is different from using eval
with code for a generator function expression.
Invoking the GeneratorFunction
constructor as a function (without using the new
operator) has the same effect as invoking it as a constructor.
Properties
GeneratorFunction.length
- The
GeneratorFunction
constructor's length property whose value is 1. GeneratorFunction.prototype
- Allows the addition of properties to all generator function objects.
GeneratorFunction
prototype object
Properties
GeneratorFunction.constructor
- The initial value is
GeneratorFunction
. GeneratorFunction.prototype.prototype
- The value is
%GeneratorPrototype%
.
GeneratorFunction
instances
GeneratorFunction
instances inherit methods and properties from GeneratorFunction.prototype
. As with all constructors, you can change the constructor's prototype object to make changes to all GeneratorFunction
instances.
Examples
Creating a generator function from a GeneratorFunction
constructor
var GeneratorFunction = Object.getPrototypeOf(function*(){}).constructor var g = new GeneratorFunction("a", "yield a * 2"); var iterator = g(10); console.log(iterator.next().value); // 20
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'GeneratorFunction' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'GeneratorFunction' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | 26 (26) | ? | ? | ? |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | ? | (Yes) | 26 (26) | ? | ? | ? |