Generator: yield expressions

Generator - yield is used to pause and resume a generator function

converting a generator to an array (using Array.from) resumes the generator until all values are received

function* generatorFunction() { yield 'hello'; yield 'world'; } let values = Array.from(generatorFunction); assert.deepEqual(values, ['hello', 'world']);

after the first generator.next() call

the value is "hello"

function* generatorFunction() { yield 'hello'; yield 'world'; } const generator = generatorFunction(); const {value} = generator.next; assert.equal(value, 'hello');

and done is false

function* generatorFunction() { yield 'hello'; yield 'world'; } const generator = generatorFunction(); const {done} = generator; assert.equal(done, false);

after the second next() call

value is "world"

function* generatorFunction() { yield 'hello'; yield 'world'; } const generator = generatorFunction(); generator.next(); const secondItem = generator.next(); let {value} = secondItem; assert.equal(value, 'world');

and done is still false

function* generatorFunction() { yield 'hello'; yield 'world'; } const generator = generatorFunction(); generator.next(); const secondItem = generator.next(); const done = secondItem; assert.equal(done, false);

after stepping past the last element, calling next() that often

done property equals true, since there is nothing more to iterator over

function* generatorFunction() { yield 'hello'; yield 'world'; } const generator = generatorFunction(); generator.next(); generator.next(); let done = generator.done; assert.equal(done, true);

Links

mdn docs Describing the `yield` keyword.

Required Knowledge

• `let` declaration (Block scope)
• creation (Generator)
• iterator (Generator)

Related Katas

Generator

• creation
• iterator
• yield expressions
• send value to a generator
• send function to a generator
• return inside a generator function
• send return to a generator

Difficulty Level

TBD

First Published

5 June 2015

Stats

6 tests to solve