Type must have a '[Symbol.iterator]()' method that returns an iterator.

[kwojcik-blockether]

TypeScript Version: 1.8.10

Code

let MyObject = {
    'a': 'Hello',
    'b': 'it\'s',
    'c': 'me',
    'd': 'you',
    'e': 'looking',
    'f': 'for'
};
MyObject[Symbol.iterator] = function* () {
    let properties = Object.keys(this);
    for (let i of properties) {
        yield [i, this[i]];
    }
}
for (let [k, v] of MyObject) {
    console.log(`Here is key ${k} and here is value ${v}`);
}

Expected behavior:
I want this code to pass without error but I do not now how can i do it.
If i try to run the .js code it works just fine and prints this output:

Here is key a and here is value Hello
Here is key b and here is value it's
Here is key c and here is value me
Here is key d and here is value you
Here is key e and here is value looking
Here is key f and here is value for

Actual behavior:
The error message is:
Type must have a 'Symbol.iterator' method that returns an iterator.

[alitaheri]

The inferred type of MyObject doesn't have an iterator. try:

let MyObject = {
    'a': 'Hello',
    'b': 'it\'s',
    'c': 'me',
    'd': 'you',
    'e': 'looking',
    'f': 'for',
    [Symbol.iterator]: function* () {
        let properties = Object.keys(this);
        for (let i of properties) {
            yield [i, this[i]];
        }
    }  
};

for (let [k, v] of MyObject) {
    console.log(`Here is key ${k} and here is value ${v}`);
}

[kwojcik-blockether]

Big thanks 👍 Now it works like a charm. Could you please tell me how it is possible that the typescript does not bind it to an object?

MyObject[Symbol.iterator] = function* () {
    let properties = Object.keys(this);
    for (let i of properties) {
        yield [i, this[i]];
    }
}

[alitaheri]

That is because type is inferred before the iterator is added.

the type of MyObject is inferred to be:

{
a: string;
b: string;
c: string;
d: string;
e: string;
f: string;
}

The type doesn't include an iterator. Typescript team is trying to fix this. take a look at their Expando Type proposal.

[mhegazy]

thanks @alitaheri!