JavaScript - Merge two arrays with different sizes

Question

I have two arrays:

var array1= [1,3,5,7,9,11]
var array2= [undefined,4,6]

I need to merge one element of the array1, then one element of the array2, etc. This is my code:

function mergeArrays(array1, array2){
    var array3 = []; 
    maxlength = Math.max(array1.length, array2.length);

for(i=0;i<maxlength;i++){   
    array3.push(array1[i]);  
    array3.push(array2[i]);
}      
    return console.log(array3);
}

The output now is:

array3 = [1,undefined,3,4,6,7,undefined,9,undefined,11,undefined]

I need the output to be:

array3 = [1,undefined,3,4,6,7,8,11]

I mean, I can't use (,= undefined). because if I have an undefined in the middle of the array it has to be there.

Answer 1

You are not placing a check for the length of shorter array. Your function is fetching a value which is higher than the length of the array, hence, extra undefined. This should do the job

 var array1 = [1, 3, 5, 7, 9, 11]; var array2 = [undefined, 4, 6]; function mergeArrays(array1, array2) { var array3 = []; maxlength = Math.max(array1.length, array2.length); for (i = 0; i < maxlength; i++) { if (i < array1.length) array3.push(array1[i]); if (i < array2.length) array3.push(array2[i]); } return console.log(array3); } mergeArrays(array1, array2);

Answer 2

Instead of checking for undefined , you could check for the array lengths, like this:

 const array1 = [1,3,5,7,9,11] const array2 = [undefined,4,6] function mergeArrays(array1, array2){ const array3 = []; const maxlength = Math.max(array1.length, array2.length); for(let i = 0; i < maxlength; i++) { if (i < array1.length) { array3.push(array1[i]); } if (i < array2.length) { array3.push(array2[i]); } } return array3; } console.log(mergeArrays(array1, array2));

Answer 3

You can grab the max length of the two arrays and loop until you hit that value. While looping, check if the length has been exceeded and push onto the result.

 const allEqual = (...args) => ((head, ...tail) => tail.every(curr => curr === head)) (args.map(v => JSON.stringify(v))); const test = ({ actual, expected }) => { console.log(JSON.stringify(actual)); console.log(allEqual(actual, expected)); }; const interlaceArrays = (...arrays) => { const result = []; const maxLen = Math.max(...arrays.map(({ length }) => length)); for (let i = 0; i < maxLen; i++) { arrays.forEach(arr => { if (i < arr.length) result.push(arr[i]); }) } return result; }; const odd = [1, 3, 5, 7, 9, 11], even = [undefined, 4, 6], other = ['a', 'b']; test({ actual: interlaceArrays(odd, even), expected: [1, undefined, 3, 4, 5, 6, 7, 9, 11] }); test({ actual: interlaceArrays(odd, even, other), expected: [1, undefined, 'a', 3, 4, 'b', 5, 6, 7, 9, 11] });

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