Error when running example code for Javascript doc - String.match() about bob HOT 7 CLOSED

Searching the ECMAScript spec for uses of OrdinaryObjectCreate(null) I find a few:

• @@unscopables properties such as [1,2,3][Symbol.unscopables]
• import.meta in modules
• The regexp named capture groups described in their issue

So it is very uncommon.

from bob.

@MEF4232 Thank you for reporting this. @wbamberg Thank you for digging in, that is indeed the problem. As this is a problem with interactive examples/Bob I am moving the issue to the mdn/bob repo

from bob.

Just to remember for later for myself (but if it's interesting to others)

• Prototype methods, objects without proto
• createMatchResultTemplateObject with Indices has groups only property and createMatchResultTemplateObject

from bob.

This is interesting. The same example works in the browser console, but fails in the interactive example's console, in both Firefox and Chrome.

Firefox: "Error: t.constructor is undefined"
Chrome: "Error: Cannot read property 'name' of undefined"

I think it's very likely that this is due to a bug in the interactive examples code that implements console.log: formatOutput is trying to work out what kind of thing it's trying to log, and if it thinks it's an object, calling formatObject. In particular it is doing:

var objectName = input.constructor.name;

...so it's assuming that if it's being called, then the argument has a constructor property. But in the browser console:

const paragraph = 'The quick brown fox jumps over the lazy dog. It barked.';

const capturingRegex = /(?<animal>fox|cat) jumps over/;
const found = paragraph.match(capturingRegex);

console.log(typeof found.groups); // "object"
console.log(typeof found.groups.constructor) // "undefined"
console.log(typeof found.groups.constructor.name) // "TypeError: found.groups.constructor is undefined"

@schalkneethling , what do you reckon?

from bob.

@schalkneethling , what do you reckon?

Will take a look. Thanks for the heads up, @wbamberg

from bob.

@wbamberg Ok, so adding this solves the problem:

if (!objectName.constructor || !objectName.prototype) {
    var formattedChild = '';
    var start = true;
    for (var key in input) {
        if (start) {
            start = false;
        } else {
            formattedChild = formattedChild + ', ';
        }
        formattedChild =
            formattedChild + key + ': ' + this.formatOutput(input[key]);
    }
    return 'Object { ' + formattedChild + ' }';
}

What I am really curious about is what type of Object this is that has neither a constructor nor a prototype. According to the docs:

All objects (with the exception of objects created with Object.create(null)) will have a constructor property

Are there other instances of this other than on String.match?

from bob.

Thank you for the extremely valuable info @karlcow and @moztcampbell ❤️

from bob.