javascript - Merging issue between array and string -

i have array containing letters , colors.

const = [     {char: 'h', color: 'red'},      {char: 'e', color: 'red'},      {char: 'y', color: 'red'},     {char: ' ', color: 'green'},     {char: 't', color: 'red'},      {char: 'h', color: 'red'},      {char: 'e', color: 'red'},      {char: 'r', color: 'red'},      {char: 'e', color: 'red'} ];  

i want write function merges string:

const s = 'hey, howdy there';

while preserving original mapping of chars colors. instance, chars compose hey , there should still red , green, painted in array a, while new chars default arbitrary, yellow , old chars deleted. so, output of function give me like:

res = [     {char: 'h', color: 'red'},      {char: 'e', color: 'red'},      {char: 'y', color: 'red'},     {char: ',', color: 'yellow'},     {char: ' ', color: 'green'},     {char: 'h', color: 'yellow'},      {char: 'o', color: 'yellow'},      {char: 'w', color: 'yellow'},      {char: 'd', color: 'yellow'},      {char: 'y', color: 'yellow'},      {char: ' ', color: 'yellow'},     {char: 't', color: 'red'},      {char: 'h', color: 'red'},      {char: 'e', color: 'red'},      {char: 'r', color: 'red'},      {char: 'e', color: 'red'} ];  

one approach might extract chars const a, join them string , split on space, have array of words. repeat string s. loop on new split array of string s until there mismatch between , original array split. happen on , char.

this i'm not sure how proceed. in simple case, there 2 words, can keep first word , replace else new words string s split. however, in case provided, i'm adding values new string (i.e. , howdy) while preserving values of old array (there).

i imagine algorithm git uses diff text work here i'm not sure how replicate it, or if efficient in use case.

edit: modified bit because realized of inconsistent.

how this?

https://jsfiddle.net/jdv9gz01/

function megajoin (orig, newword, index) { var tmparr = orig.slice();     var newwordarray = newword.split('').map((char)=>{return {char:char, color:'yellow'}});   array.prototype.splice.apply(tmparr, [index,0].concat(newwordarray));   return tmparr; } 

i unsure join should happen, function uses index know should join.

if don't know newword is, function it. it's not perfect tho.

function getdifference(weirdarray, newstring) {     var tmps = [];     (var = 0; <= weirdarray.length; i++) {         var word = a[i];         if (word && word.char !== '' && !== a.length) {             tmps.push(word.char);         } else {             newstring = newstring.replace(tmps.join(''), '');             tmps = [];         }     }     return newstring; }