how to add key value pair in the JSON object already declared

Could you do the following:

obj = {
    "1":"aa",
    "2":"bb"
};


var newNum = "3";
var newVal = "cc";


obj[newNum] = newVal;



alert(obj["3"]); // this would alert 'cc'

Object assign copies one or more source objects to the target object. So we could use Object.assign here.

Syntax: Object.assign(target, ...sources)

var obj  = {};

Object.assign(obj, {"1":"aa", "2":"bb"})

console.log(obj)

You can use dot notation or bracket notation ...

var obj = {};
obj = {
  "1": "aa",
  "2": "bb"
};

obj.another = "valuehere";
obj["3"] = "cc";

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