Search And Replace Through Array?

i have a implementation where i need to perform a search and replace. i will try to explain to the best of my ability. i have a variable, var a = "THIS IS SOME SOME TEXT";

then i have another array variable, var b = new Array(); which contains elements in key=value format eg. SOME=NEWSOME so what i need to do is, i need to loop through this array and if SOME exists in var a, then i need to replace it with NEWSOME. so for each value before =, if it exists in var a replace it with whats after =. and replace only once, so if SOME exists multiple times just replace the first occurence.

so essentially my final string would be, THIS IS NEWSOME SOME TEXT.