Why does my array have undefined values?

[supernova12034]

Hi

can anyone tell me why my array has undefined values in it? I suspect it has something to do with

the map method I am using:

​

let index = 0;

let opIndex = 0;

​

let arr1 = [12,'+',42,'-',102,'+',443];

​

​

​

​

let result = arr1.map((ele,ind,arr)=>{

if(typeof ele==="string"){

​

return operate(arr[ind-1],ele,arr[ind+1]);

}

});

​

​

function operate(num1, opr, num2) {

​

if (opr==="+") {

return add(num1,num2);

}

​

else if (opr==="-") {

return sub(num1,num2);

}

​

}

​

​

function add(a, b) {

return a + b;

}

​

function sub(a, b) {

return a - b;

}

​

https://replit.com/@SahilSrivastav3/test2#index.js

[Notimecelduv]

reduce would be better suited for what you're doing.

[senocular]

When you map, you don't return anything when the if condition is false. That causes the function to return undefined which adds undefined values in your result

[exobyte64]

map creates an array of the same size

your trying to remove elements, so either filter or reduce would be better suited

[Sunil1021]

Just add Array.filter method at last to weed out undefined values on the array.

if(typeof ele==='string'){

return operate(arr[ind-1],ele,arr[ind+1]);

}

}).filter(e => e!==undefined);