Javascript Callback function in loop

Question

I've 3 functions in Javascript. function1 insert data into an array-array_message', function2 export the 'array_message' into a csv file. The function3 call these two functions with all the elements in a list.

In Javascript, function2 is executed at the same time as function1, which makes that the exported file is always empty because no time to fill in the 'array_message'.

Could anyone help how to call function2 when function1 is done in this 'for' loop? Maybe another callback function?

 function function3(){
      for (var i=0; i<list.length;i++){
        console.log(list[i]);
        function1(list[i])
        function2(list[i]+'.csv',array_message)
      }
     }

Wrong approach. Seems that all your the functions struggling to get and use a global sate which is the source of your problems. You can make them pure. Pure functions take input and produce output and don't have side effects, so function1 needs to accept that list[i] item and produce the array_message object, which function2 consumes afterwards, thus you can chain them more easily. — VLAZ
– VLAZ, Commented Aug 10, 2016 at 16:23

Rob M. · Accepted Answer · 2016-08-10 16:24:35Z

2

You could utilize Promises (preferrable IMO) or a callback to accomplish this:

function function1(item) {
    return new Promise(function(resolve, reject) {
        // do operations
        if (operationSuccessful) {
            resolve(dataFromOperation);
        } else {
            reject(errorFromOperation);
        }
    });
}

function function3() {
    for (var i=0; i<list.length;i++) {
        // only call function2 after function1 is complete
        function1(item[i]).then(function(responseData) {
            function2(responseData);
        }).catch(function(error) {
            console.error("Problem in function1")
        });
    }
}

answered Aug 10, 2016 at 16:24

Rob M.

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