Removing undefined values from Array

Inline using lambda

result.filter(item => item);

You can use lodash compact method, which removes null, undefined and ''.

_.compact(data)

[NaN, undefined, null, 0, 1, 2, 2000, Infinity].filter(Boolean)
//[ 1, 2, 2000, Infinity ]

If you have an array of objects and want to remove all null and undefined items:

[].filter(item => !!item);

ES6 single line

data.filter(e => e)

data.filter(Boolean)

Is the most short and readable way to do it.

As Diogo Capela said, but where 0 is not filtered out as well.

[].filter(item => item !== undefined && item !== null)

in ES6 this can be achieved by simply using using filter with function return the value like this:

const array = [NaN, 0, 15, false, -22, '',undefined, 47, null];
const filteredArr = array.filter(elm => elm);
console.log(filteredArr);

var a =  ["3","", "6"];
var b =  [23,54,56];
var result = [];

for (var i=0;i<a.length;++i) {
    if (a[i] != "") {
        result[i] = b[i];
    }
}

result = result.filter(function( element ) {
   return element !== undefined;
});

console.log(result);

Array.prototype.reduce() can be used to delete elements by condition from an array but with additional transformation of the elements if required in one iteration.

Remove undefined values from array, with sub-arrays support.

function transform(arr) {
    return arr.reduce((memo, item) => {
        if (typeof item !== "undefined") {
            if (Array.isArray(item)) item = transform(item);
            // We can transform item here.
            memo.push(item);
        }
        return memo;
    }, []);
}

let test1 = [1, 2, "b", 0, {}, "", , " ", NaN, 3, undefined, null, 5, false, true, [1, true, 2, , undefined, 3, false, ''], 10];

console.log(transform(test1));

Try it on jsfiddle.net/bjoy4bcc/

var arr1 = [NaN, 0, 15, false, -22, '',undefined, 47, null];

var array1 = arr1.filter(function(e){ return e;});

document.write(array1);

single lined answer

The solution with Array.filter will actually keep the array unchanged and create a new array without the undesired items. If you want to clean an array without duplicating it, you can use this:

for (var i = data.length-1; i >= 0; i--) {
    if (!data[i]) {
        data.splice(i, 1);
    }
}

If you are in Typescript and want to return an Array of strings vs from Array<string|undefined> try one of these...

var arr = ['a', 'b', 'c', undefined, 'e', undefined, 'g'];
var solutionA = arr.reduce((acc, item) => {
    item && acc.push(item);
    return acc;
}, []);

console.log('solution a', solutionA);

var solutionB = [];
arr.forEach((each) => each && solutionB.push(each), []);

console.log('solution b', solutionB);

arr.forEach((each,index) => (!each) && arr.splice(index,1),[]);
console.log('solution c', arr);

In the Qt - JS implementation:

The filter does not select undefined because it does not hit the lambda so the usual for...of turned out to be preferable:

// B_half.filter(n => { return n !== undefined  })
// B_half.filter(n => n)
// B_half.filter( (n) => { console.log(n); return n })

tree_order = A_half // .concat( B_half )

for ( let ins of B_half ) 
{ 
  if (ins !== undefined) 
  {
    tree_order.push(ins); 
  } 
}