Popular:
 Building Resilient Systems on AWS: Learn how to design and implement a resilient, highly available, fault-tolerant infrastructure on AWS.

Fill an Array with Sequential Values

By  on  

I've been contributing to Mozilla's awesome DevTools debugger because, well, I want to give back to the Firefox Engineers and all the developers who have stayed loyal to Firefox.  Having my hand in loads of Mozilla projects is really satisfying, especially for my ego.

In any event, one task required me to fill an array with every number in a sequence, then I would filter out unwanted items based on another array.  Here's how you can fill a range within an array:

const fillRange = (start, end) => {
  return Array(end - start + 1).fill().map((item, index) => start + index);
};

const allLines = fillRange(0, numLines - 1);

// [0, 1, 2, 3, 4, 5, ...]

From there I could filter out what I didn't want:

let executableLines = [/* series of line numbers with code */];
const emptyLines = allLines.filter(i => !executableLines.includes(i));

When the feature gets merged (...and no one complains about their Firefox debugger...) I'll share more about  my contribution!

Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring

Recent Features

Incredible Demos

  • By
    CSS Ellipsis Beginning of String

    I was incredibly happy when CSS text-overflow: ellipsis (married with fixed width and overflow: hidden was introduced to the CSS spec and browsers; the feature allowed us to stop trying to marry JavaScript width calculation with string width calculation and truncation.  CSS ellipsis was also very friendly to...

  • By
    Introducing MooTools NextPrev

    One thing I love doing is duplicating OS functionalities. One of the things your OS allows you to do easily is move from one item to another. Most of the time you're simply trying to get to the next or the previous item.

Discussion

  1. Tracy-Gregory Gilmore

    Would the instruction 

    const allLines = fillRange(0, numLines - 1);

    not result in an array starting with zero as the first value?

    • David Walsh

      Yes, you’re right! I’ve updated the post!

  2. Jorge Ortega

    Nice! Thanks to this post I could do this:

    // Array of 24 hours string values ['00'...'23']
const hours = Array(24).fill().map((item, index) => index < 10 ? 0${index} : ${index})

// Array of 60 minutes string values ['00'...'59']
const minutes = Array(60).fill().map((item, index) => index < 10 ? 0${index} : ${index})
  3. Luca Borrione

    Great post! Little contribution:

    const fillRange = (start, end) => {
	return [...Array(end - start + 1)].map((item, index) => start + index);
}
    • Tracy-Gregory Gilmore

      Using an arrow function with a single expression does not require a return statement or statement block. Thus, the line of code above could be reduced to.

      const fillRange = (start, end) => 
   [...Array(end - start + 1)].map((item, index) => start + index);
  4. Nicolás Casanova

    This is great, but, one question. If I want to have a list with decimals numbers, how can I do it?
    example: 0.1 to 5.0. (resp: 0.1, 0.2, 0.3 … 4.8, 4.9, 5)
    How can I do this?
    Thanks! :D

    • MR T-G J GILMORE

      You could always map() the output of fillRange.

      const decimals = fillRange(0, 50).map(int => int / 10);
    • MR T-G J GILMORE

      That should have been 1 to 51:

      const decimals = fillRange(1, 51).map(int => int / 10);

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!