Change variables value inside nested function

Question

I have function that loops and inside that function I call another function (which should change "newArray[x]" value, but it doesn't do anything).

function UTF8() {
        newArray = ["0011", "0001"]
        newArray.forEach(x => {
            binaryToHexadecimal(newArray[x]);
            console.log(newArray[x])
        });
        console.log(newArray[0])
}

function binaryToHexadecimal(string) {
    if (string === "0000") {
        return string = "0";
    }
    else if (string ==="0001") {
        return string = "1";
    }
    else if (string ==="0010") {
        return string = "2";
    }
    else if (string ==="0011") {
        return string = "3";
    }
    else if (string ==="0100") {
        return string = "4";
    }

}
UTF8();

arguments are called by value. Assigning a new value to the parameter never changes the variable or property that you pass as argument. — trincot
– trincot, Commented Oct 26, 2020 at 18:40
1. newArray[x] is undefined because x will be either 0011 or 0001 and both newArray["0011"] and newArray["0001"] don't exist. 2. that's not how you replace a value from an array — ibrahim mahrir
– ibrahim mahrir, Commented Oct 26, 2020 at 18:40
1) you're using forEach, so x isn't the index, it's the array element itself 2) you would have to use newArray[x] = binaryToHexadecimal(newArray[x]); 3) this is precisely what .map() is for — user5734311
– user5734311, Commented Oct 26, 2020 at 18:40
["0011", "0001"].map(b => parseInt(b, 2).toString(16).toUpperCase()); — epascarello
– epascarello, Commented Oct 26, 2020 at 18:41

David · Accepted Answer · 2020-10-26 18:41:41Z

2

The function is setting a local variable, it has no control over whatever variable was used to pass that value.

Just return the value you want from the function. For example:

return "0";

Then when calling the function, use that value to set your array element as needed:

newArray[x] = binaryToHexadecimal(newArray[x]);

answered Oct 26, 2020 at 18:41

David

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Sarun UK · Accepted Answer · 2020-10-26 18:44:41Z

2

Use map instead of forEach.

And here return string = "0"; you can directly return the value.

function UTF8() {
        newArray = ["0011", "0001"]
        return newArray.map(x => {
            return binaryToHexadecimal(x);
        });
}

function binaryToHexadecimal(string) {
    if (string === "0000") {
        return "0";
    }
    else if (string ==="0001") {
        return "1";
    }
    else if (string ==="0010") {
        return "2";
    }
    else if (string === "0011") {
        return "3";
    }
    else if (string ==="0100") {
        return string = "4";
    }

}
const result = UTF8();
  console.log(result);

answered Oct 26, 2020 at 18:44

Sarun UK

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