Arrow function error: Object is not a function

Question

When I try to use an arrow function with {} it seems to think it's an object and throw an error. I thought this is how arrow functions are generally defined?

The error given for the code below is TypeError: #<Object> is not a function

let allProperties = [];

sites.forEach(site => site.properties.forEach(p => {if (!allProperties.find(p)) allProperties.push(p)} ));

Edit: sites might be defined similarly to the following:

sites = [
{
    "properties": [
        { "id": "111-11", "display": "Zone", "value": 1 },
    ]
}];

What is sites? Please post a snippet which can reproduce your error. — Michał Perłakowski
– Michał Perłakowski, Commented Aug 19, 2016 at 22:11
If you use the {} with => you need to use the return statement. It only implicitly returns the value if you provide a single expression after =>, not if you provide a block — mhodges
– mhodges, Commented Aug 19, 2016 at 22:25
Thank you, that explains the discrepancy. I'm not really trying to return anything though, just push to a new list. I'm new to JavaScript and I'm a little confused. — wtblife
– wtblife, Commented Aug 19, 2016 at 22:26
Did that fix your problem? I wasn't sure if it would, I just wanted to explain that bit of functionality because in your question you seemed unsure of how it worked. — mhodges
– mhodges, Commented Aug 19, 2016 at 22:27
After thinking over it for a second I still don't know where to go. My goal isn't to return a value, but rather push a value to an array while inside the function. I edited my comment as you posted, sorry. — wtblife
– wtblife, Commented Aug 19, 2016 at 22:33

ASDFGerte · Accepted Answer · 2016-08-19 22:40:27Z

1

Array.prototype.find expects a callback function as first parameter, which is not what you supply and probably not thought of.

answered Aug 19, 2016 at 22:40

ASDFGerte

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1 Comment

wtblife Over a year ago

Ya this was apparently the issue. I appreciate the help!

mhodges · Accepted Answer · 2016-08-19 22:42:49Z

0

It's barking at if(!allProperties.find(p)). It's not liking the .find() because you have supplied it with an object as a parameter, not a function. .find() Docs Here

If you change it to if (allProperties.indexOf(p) === -1) {...} it works as expected.

var allProperties = [];
var sites = [
{
    "properties": [
        { "id": "111-11", "display": "Zone", "value": 1 },
    ]
}];

sites.forEach(site => site.properties.forEach(p => {
	if (allProperties.indexOf(p) === -1) {
		allProperties.push(p);
	}
}));

console.log(allProperties);

edited Aug 19, 2016 at 22:42

answered Aug 19, 2016 at 22:37

mhodges

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4 Comments

wtblife Over a year ago

Ohhh I think find wants a function, not an object to match with.

wtblife Over a year ago

Thanks for the help!

Barmar Over a year ago

I think the function you want is allProperties.contains(p). But this is recent, so older browsers won't support it.

mhodges Over a year ago

@Barmar Can you post documentation for .contains()? I see array.prototype.includes(), but I can't seem to find .contains() anywhere

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