Chapter 1: Introducing ECMAScript 6
Activity 1 – Implementing Generators
You have been tasked with building a simple app that generates numbers in the Fibonacci sequence upon request. The app generates the next number in the sequence for each request and resets the sequence it is given an input. Use a generator to generate the Fibonacci sequence. If a value is passed into the generator, reset the sequence. You may start the Fibonacci sequence at n=1 for simplicity.
To highlight how the generators can be used to build iterative datasets, follow these steps:
Look up the Fibonacci sequence and understand how the next value is calculated.
Create a generator for the Fibonacci sequence.
Inside the generator, set up the default values for
currentandnext(0, 1) using variablesn2andn1.Create an infinite
whileloop.Inside the
whileloop, use theyieldkeyword to provide the current value in the sequence and save the return value of the yield statement into a variable calledinput.If input contains a value, reset the variables
n2andn1to their starting values.Inside the
whileloop, calculate the new next value fromcurrent+nextand save it into the variable next.Otherwise update
n2to contain the value fromn1(thenextvalue) and setn1to thenextvalue that we calculated at the top of thewhileloop.
Code:
index.jsfunction* fibonacci () {
let n2 = 0;x
let n1 = 1;
while ( true ) {
let input = yield n2;
if ( input ) {
n1 = 1;
n2 = 0;
} else {
let next = n1 + n2;
[ n1, n2 ] = [ next, n1 ];
}
}
}
let gen = fibonacci();Snippet 1.87: Implementing a generator
Outcome:
Figure 1.19: Fibonacci sequence with a generator
You have successfully demonstrated how generators can be used to build an iterative data set based on the Fibonacci sequence.
