How to set value to json object from another json object?

Assuming same order:

var setvalue="";
var a = [{id: "Make",   seqNo: 4},
         {id: "Model",  seqNo: 1},
         {id: "XModel", seqNo: 2},
         {id: "Rate",   seqNo: 3},
         {id: "Price",  seqNo: 0}];

var b = [{id: "Make", field: "make", seqNo: setvalue},
         {id: "Model", field: "model", seqNo: setvalue},
         {id: "XModel", field: "model", seqNo: setvalue},
         {id: "Rate", field: "price", seqNo: setvalue},
         {id: "Price", field: "price", seqNo: setvalue}
        ];

var c=[];
for (var i=0;i<a.length;i++) {
  var aItem = a[i], bItem=b[i];
  c.push({ headerName:aItem.id, field:bItem.field, seqNo: aItem.seqNo });
}
console.log(c);
document.write(JSON.stringify(c, null, 2).replace(/},/g,"},<br/>"));

I would try something like this:

var mapped_a = a.reduce(function(result, element) {
    result[element.id] = element.seqNo;
    return result;
}, {});

// mapped_a => {Make: 4, Model: 1,.. }

var mapped_b = b.map(function(element) {
    var newElement = {
        id: element.id,
        field: element.field,
        seqNo: mapped_a[element.id]
    };
    return newElement;
});

In the first step I convert the array to an object map. Then I can access the correct element via the array syntax in the map function.

here is the looping solution assuming you have equal number of objects in both array to get the satisfying result

var a = [{id: "Make",   seqNo: 4},
            {id: "Model",  seqNo: 1},
            {id: "XModel", seqNo: 2},
            {id: "Rate",   seqNo: 3},
            {id: "Price",  seqNo: 0}];

var b = [
           {id: "Make", field: "make", seqNo: 'setvalue'},
           {id: "Model", field: "model", seqNo: 'setvalue'},
           {id: "XModel", field: "model", seqNo: 'setvalue'},
           {id: "Rate", field: "price", seqNo: 'setvalue'},
           {id: "Price", field: "price", seqNo: 'setvalue'}
        ];

b = b.map(function (obj) {
    a.forEach(function (aObj,aIndex) {
        if (obj.id == a[aIndex].id) {
            obj["seqNo"] = a[aIndex].seqNo;
        }
    })
    return obj;
})
console.log(b)

// Sample result
[ { id: 'Make', field: 'make', seqNo: 4 },
  { id: 'Model', field: 'model', seqNo: 1 },
  { id: 'XModel', field: 'model', seqNo: 2 },
  { id: 'Rate', field: 'price', seqNo: 3 },
  { id: 'Price', field: 'price', seqNo: 0 } ]

If you're using underscorejs you should use the following code for merge two objects

_.extend({id: "Make", field: "make", seqNo: setvalue}, {id: "Make", seqNo: 4})

If you're using Jquery then this code

$.extend({id: "Make", field: "make", seqNo: setvalue}, {id: "Make", seqNo: 4})

If you need a plain javascript function you can find it at: http://youmightnotneedjquery.com/

So, you have two arrays of objects, so you need use map or another method to go through your array and apply for each element the extending function.

Thanks for this challenging question.

This is my solution using lodash:

var c = _.zipWith(b, a, function(obj1, obj2) {
    var object= _.assign({}, obj1, obj2);
    object.headerName = object.id; 
    delete object.id; 
    return object;
});

console.log(c);

Here is Your code :

var a = [{id: "Make",   seqNo: 4},
        {id: "Model",  seqNo: 1},
        {id: "XModel", seqNo: 2},
        {id: "Rate",   seqNo: 3},
        {id: "Price",  seqNo: 0}];

// make it null of seqNo
var b = [
       {id: "Make", field: "make", seqNo: null},
       {id: "Model", field: "model", seqNo: null},
       {id: "XModel", field: "model", seqNo: null},
       {id: "Rate", field: "price", seqNo: null},
       {id: "Price", field: "price", seqNo: null}
    ];

Set Value here

Just Make it :

   if(a.length == b.length){
      for(var i=0; i<a.length;i++){
         b[i].seqNo = a[i].seqNo;
      }
    }
    else{ console.log('Error','length not Match')}

Also Alternate Way :

You can assign directly if you have a two object:

var b = [
       {id: "Make", field: "make", seqNo: a[0].seqNo},
       {id: "Model", field: "model", seqNo: a[1].seqNo},
       {id: "XModel", field: "model", seqNo: a[2].seqNo},
       {id: "Rate", field: "price", seqNo: a[3].seqNo},
       {id: "Price", field: "price", seqNo: a[4].seqNo}
    ]; 

Hope this help for you...

I suggest using for loop in javascript.

var a = [{id: "Make",   seqNo: 4},
        {id: "Model",  seqNo: 1},
        {id: "XModel", seqNo: 2},
        {id: "Rate",   seqNo: 3},
        {id: "Price",  seqNo: 0}];
var b = [
       {id: "Make", field: "make", seqNo: 0},
       {id: "Model", field: "model", seqNo: 0},
       {id: "XModel", field: "model", seqNo: 0},
       {id: "Rate", field: "price", seqNo: 0},
       {id: "Price", field: "price", seqNo: 0 }
    ];
for (var iB in b) {
   for(var iA in a){

   var objB = b[iB];
   var objA = a[iA];
        if(objB.id == objA.id ){
          objB.seqNo = objA.seqNo;
        }
    }
}
console.log(b)

JSfiddle Link

Hope it helps.