Mr Speaker


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“let” is the new “with”. But good.

The ES2015's let and const keywords give us better (actually useful!) control over variable scope. We can use this to write code in a more terse, cleaner manner.

Mozilla's original implementation of let had support for non-standard let blocks that looked like this:

let (x = x+10, y = 12) {
  console.log(x+y); // 27
}

Let blocks also allowed us to define blocks similar to how we used to write with in the olden days: let (pos = obj.position) { pos.x++; }. I don't know why this got the boot from the final ES6 spec (I quite like the syntax), but we can recreate the idea using empty blocks and defining the variables like normal:

const stats = new Stats();
{
  const dom = stats.domElement;
  const style = dom.style;
  stats.setMode( 0 );
  style.left = "0px";
  style.top = "0px";
  document.body.appendChild( dom );
}

Thanks to const and let behaving sensibly, the dom and style are only defined inside the block. This gives us all the power of the let block, and none of the problems of the old school with statement.


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