CODEWITHSUNDEEP
javascriptpromise
HAZRD
HAZRD

Reputation: 63

How to wait on an array being filled by another promise

d3 is loading a Global array. I want to call that data in another function.

I don't understand promises very well and I can't decipher documentation.

First function called does:

d3.tsv( ... ).then(function(data){Loaded_Data[0]=data);}

Then a function is called to populate my svg:

svg.getElementById("example") = Loaded_Data[0][Loaded_Data[0].length-1]['Example Column']

I just can't figure out how to code: "Promise me that there is data in this Array, then do the value assignment"

Please be as explicit and obvious as possible. Thank you.

Upvotes: 1

Views: 165

Answers (2)

Ramaraja
Ramaraja

Reputation: 2626

You can use the ES8 feature async/await, Let's imagine that you are executing your logic in a function called foo,

// If you are using await inside a function it should be declared as async
async function foo(){

// await will make sure to pause the execution till the promise is resolved
Loaded_Data[0]=await d3.tsv( ... );

svg.getElementById("example") = Loaded_Data[0][Loaded_Data[0].length-1]['Example Column'] 

}

For more on async/await, here is a great article,

https://alligator.io/js/async-functions/

Upvotes: 1

Zze
Zze

Reputation: 18805

If your 2 code snippets are in the same .js file then you can likely just do:

d3.tsv( ... ).then(function(data){
    Loaded_Data[0]=data;
    svg.getElementById("example") = Loaded_Data[0][Loaded_Data[0].length-1]['Example Column'];
}

If this is not the case, then you could use an Observable, or you could trigger a custom Event that is called from within your .then.

d3.tsv( ... ).then(function(data){
     Loaded_Data[0]=data;
     var event = new Event('Loaded_Data_HasData');
     window.dispatchEvent(event);
}

and then in your other file / location, listen for that event. 

elem.addEventListener('Loaded_Data_HasData', function (e) { 
    svg.getElementById("example") = Loaded_Data[0][Loaded_Data[0].length-1]['Example Column']; 
}, false);

Upvotes: 1

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