如何更改ES5-> ES8 JS函数语法？

Question

I try to change this (working well) function to be able to run with node + ES8 (without the keyword function), but I can't figure out how to do this.

window.getElementsByXPath = function getElementsByXPath(expression, scope) {
    scope = scope || document;
    var nodes = [];
    var a = document.evaluate(expression, scope, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
    for (var i = 0; i < a.snapshotLength; i++) {
        nodes.push(a.snapshotItem(i));
    }
    return nodes;
};

(this is a file sourced from node.js to use with puppeeter + chrome headless)

Answer 1

Just remove the keyword function and function name as follow:

window.getElementsByXPath =  (expression, scope) => {
  scope = scope || document;
  var nodes = [];
  var a = document.evaluate(expression, scope, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
  for (var i = 0; i < a.snapshotLength; i++) {
    nodes.push(a.snapshotItem(i));
  }
  return nodes;
};

This is called: Arrow function.

Resource

• Arrow functions

Answer 2

Use the arrow function syntax: var foo = (param) => { // Do stuff }

With your code:

window.getElementsByXPath = (expression, scope) => {
    scope = scope || document;
    var nodes = [];
    var a = document.evaluate(expression, scope, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
    for (var i = 0; i < a.snapshotLength; i++) {
        nodes.push(a.snapshotItem(i));
    }
    return nodes;
};

Answer 3

If you want to go all the way, you could use the iterator type instead of snapshot, make an immediately executing generator, and use the spread and short arrow expression syntax.

window.getElementsByXPath = (expression, scope) =>
    [...(function * (iter, node) {
        while (node = iter.iterateNext()) yield node;
    })(document.evaluate(expression, scope || document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null))];

Not that this makes it more readable though...

The function keyword reappears, as generators can currently not be written with arrow syntax.