JS merge two objects (interview questions)

const a ={
    a:1,b:2}
const b ={
    b:1,c:2}
//  Merging two objects 
function extend(target,source){
    
    for (const key in source) {
    
        target[key] = source[key]
    }
    return target
}
console.log(extend(a,b))