Javascript function to merge / combine two URLSearchParams

Question

I am wondering what is the best most efficient code in Javascript to merge two URLSearchParams, but where one of them has higher priority, let me explain with two examples.

const oldParams = 'foo=one&coo=two'
const newParams = 'roo=three&moo=four'

urlCombine(oldParams, newParams) returns foo=one&coo=two&roo=three&moo=four

So far so good , but let's say we also want to give newParams higher priority so that if the same key exist in both newParams and oldParams the return value should always use the value of newParams , for example.

const oldParams = 'foo=one&coo=two'
const newParams = 'coo=three&foo=four'

urlCombine(oldParams, newParams) returns foo=four&coo=three

Answer 1

Use URLSearchParams to parse the strings into key-value pairs and then combine them.

 const oldParams = 'foo=one&coo=two' const newParams1 = 'roo=three&moo=four' const newParams2 = 'coo=three&foo=four' function urlCombine(a,b,overwrite=false){ a = new URLSearchParams(a); const fn = overwrite? a.set: a.append; for(let [key, value] of new URLSearchParams(b)){ fn.call(a, key, value); } return a.toString(); } console.log(urlCombine(oldParams, newParams1)); console.log(urlCombine(oldParams, newParams2, false)); console.log(urlCombine(oldParams, newParams2, true));