JavaScript labeled statement

Planted: February 27, 2024

Seen in Bytes yesterday:

Nested loops aren’t ideal, but sometimes they’re unavoidable. Given the nested loop below, how can we break out of the nested loop when j === 2?

loop.js


function loop() {
  for (let i = 0; i < 4; i++) {
    for (let j = 0; j < 4; j++) {
      if (j === 2) {
        // Break out here
      }
    }
  }
}

The tl;dr is that you can label the outer for loop:

labeledLoop.js


function loop() {
  dance: for (let i = 0; i < 4; i++) {
    for (let j = 0; j < 4; j++) {
      if (j === 2) {
        break dance;
      }
    }
  }
}

You can only use statement labels with break and continue, which I don't find myself using too often to begin with. You can't even console log a label—I tried, and it throws Uncaught ReferenceError: <label> is not defined.

I'll admit that I actually learned about labeled statements a year or two ago when reviewing a coworker's PR, but I haven't come across one since. I think it's a neat language feature to stash in my back pocket.

Reply

Respond with your thoughts, feedback, corrections, or anything else you’d like to share. Leave your email if you’d like a reply. Thanks for reading.