False positive W024: Expected an identifier and instead saw 'yield' (a reserved word)

[Andrew-Cottrell]

In ES3, yield is neither a keyword nor a future reserved word; and since ES5, keywords may be used as object property keys.

As far as I know, the code below is valid in ES3, ES5, and all later editions

/*jshint esversion: 3 */
(function () {
    "use strict";
    console.log( { yield: 0 } );
}());

However, https://jshint.com/ — currently using JSHint version 2.12.0 — reports

One warning
4 | Expected an identifier and instead saw 'yield' (a reserved word).

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A potential fix is to modify the following line in function optionalidentifier

jshint/src/jshint.js

Line 1766 in c13c5cc

if (state.inES5()) {

to

      if (state.inES5() || val === "yield") {

[jugglinmike]

Confirmed. Anyway, thanks for the report!

Other curiosities:

• this depends on ES5's strict mode
• let in the same position is tolerated (that's correct, but unexpected given the reported bug)

I'm labeling this as low-priority because I've seen very little evidence of anyone targeting ES3 these days. I'd love to hear more about your use case, though!

[Andrew-Cottrell]

I'm labeling this as low-priority because I've seen very little evidence of anyone targeting ES3 these days.

I'm happy for this issue to be low-priority. A realistic workaround is simply to not use the esversion: 3 option.

I'd love to hear more about your use case, though!

Thanks for the interest; although sadly my use case is not particularly exciting!

Many years ago I wrote a library that needed to be compatible with IE 8, and also with YUI Compressor version 2.4.8 (no ES5 support), due to a built-in minification framework used by a content management system. Fortunately, these restrictions no longer apply, but I do still need to support IE 11 and the CMS's build system & minification framework makes use of a transpiler awkward. However, I have not yet had any particular reason to use ES5 syntax; so I have continued to maintain compatibility with ES3 browsers, although this is no longer necessary. The library includes a function that implements a cross-browser equivalent of generator objects, which enables me to use modern JavaScript idioms. The term "yield" is used by generator-context objects passed to generator-body functions.

For example, the library enables the following to work in ES3 compatible browsers

/**
 * Generator functions return generator objects, which implement Iterable and Iterator.
 * @return {!Generator<number>} A non-null generator of numbers.
 */
function fibonacciNumbers() {
    var memo = [1, -1]; // create the initial state (e.g. a vector of "negafibonacci" numbers)
    return generator(function (context) { // repeat indefinitely
        memo = [memo[0] + memo[1], memo[0]]; // update the state on each evaluation
        context.yield(memo[0]); // yield the next value and suspend execution until resumed
    });
}

var count = 0;
for_of(fibonacciNumbers(), function (number, break_) {
    count += 1;
    console.log(count, number);
    if (count === 16) break_();
});

which is equivalent to the modern syntax

/**
 * Generator functions return generator objects, which implement Iterable and Iterator.
 * @return {!Generator<number>} A non-null generator of numbers.
 */
function* fibonacciNumbers() {
    let memo = [1, -1]; // create the initial state (e.g. a vector of "negafibonacci" numbers)
    while (true) { // repeat indefinitely
        memo = [memo[0] + memo[1], memo[0]]; // update the state on each evaluation
        yield memo[0]; // yield the next value and suspend execution until resumed
    }
}

let count = 0;
for (let number of fibonacciNumbers()) {
    count += 1;
    console.log(count, number);
    if (count === 16) break;
}

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A big thank you for maintaining the JSHint project; I use it almost every weekday and sometimes at weekends!