Modify object property in an array of objects

var foo = [{ bar: 1, baz: [1,2,3] }, { bar: 2, baz: [4,5,6] }];

var filtered = $.grep(foo, function(v){
    return v.bar === 1;
});

console.log(filtered);

http://jsfiddle.net/98EsQ/

Is there any way to modify a certain objects property (like the one I'm filtering out above) without creating new arrays and/or objects?

Desired result: [{ bar: 1, baz: [11,22,33] }, { bar: 2, baz: [4,5,6] }]

.map with spread (...) operator

var result = foo.map(el => el.bar == 1 ? {...el, baz: [11,22,33]} : el);

Sure, just change it:

With jQuery's $.each:

$.each(foo, function() {
    if (this.bar === 1) {
        this.baz[0] = 11;
        this.baz[1] = 22;
        this.baz[2] = 33;
        // Or: `this.baz = [11, 22, 33];`
    }
});

With ES5's forEach:

foo.forEach(function(obj) {
    if (obj.bar === 1) {
        obj.baz[0] = 11;
        obj.baz[1] = 22;
        obj.baz[2] = 33;
        // Or: `obj.baz = [11, 22, 33];`
    }
});

...or you have other looping options in this other SO answer.

You can use find and change its property.

let foo = [{ bar: 1, baz: [1,2,3] }, { bar: 2, baz: [4,5,6] }];

let obj = foo.find(f=>f.bar==1);
if(obj)
  obj.baz=[2,3,4];
console.log(foo);

Without jQuery and backwards compatibility

for (var i = 0; i < foo.length; i++) {
    if (foo[i].bar === 1) {
        foo[i].baz = [11,12,13];
    }
}

We can also achieve this by using Array's map function:

 foo.map((obj) => {
   if(obj.bar == 1){
     obj.baz[0] = 11;
     obj.baz[1] = 22;
     obj.baz[2] = 33;
   }
 })

    const objArr = [
        {prop1: 'value1', prop2: 'value11'},
        {prop1: 'value2', prop2: 'value22'},
        {prop1: 'value3', prop2: 'option33'},
        {prop1: 'value4', prop2: 'option44'}
    ]

    const newObjArr = objArr.map(obj => {
            if (['value1', 'value2'].includes(obj.prop1)) {
                return {...obj, prop1: 'newValue'}
            }
            return obj
        }
    )
    
    // const responseGotten = [
    //     { prop1: 'newValue', prop2: 'value11' },
    //     { prop1: 'newValue', prop2: 'value22' },
    //     { prop1: 'value3', prop2: 'option33' },
    //     { prop1: 'value4', prop2: 'option44' }
    // ]

$.each(foo,function(index,value)
{
    if(this.bar==1)
    {
this.baz[0] = 11;
        this.baz[1] = 22;
        this.baz[2] = 33;
    }

});

but for loop is faster than $.each so u can try to use

for(var i=0; i <foo.length; i++)
{

if(foo[i].bar==1)
{
//change the code
}
}

But before opting any of the mentioned techniques please keep in mind the performance challenges associated with each of the approach.

Object iterate For-In, average: ~240 microseconds.

Object iterate Keys For Each, average: ~294 microseconds.

Object iterate Entries For-Of, average: ~535 microseconds.

Reference - 3 JavaScript Performance Mistakes You Should Stop Doing

you can play around:

const tasks = [ { id: 1, done: false }, { id: 2, done: false } ]
const completed_task = { id: 1, done: true }

const markCompleted = (tasks, task) => {
  const index = tasks.findIndex(t => t.id === task.id);
  tasks.splice(index, 1);
  tasks.push(task);
  return tasks;
}

console.log(tasks)
console.log(markCompleted(tasks, completed_task))

EDIT

to avoid index change:

const markCompleted = (tasks, task) => {
      const index = tasks.findIndex(t => t.id === task.id);
      tasks[index] = task;
      return tasks;
    }

You can modify the array by using simple for loop

var foo = [{ bar: 1, baz: [1,2,3] }, { bar: 2, baz: [4,5,6] }];
for(i = 0;i < foo.length;i++){
  //Here your confition for which item you went to edit
	if(foo[i].bar == 1){
    //Here you logic for update property
		foo[i].baz= [1,11,22]
	}
}
console.log(foo);

You can make use of filter function of javascript.

obj = [
    {inActive:false, id:1},
    {inActive:false, id:2},
    {inActive:false, id: 3}
];
let nObj = obj.filter(ele => {
    ele.inActive = true;
    return ele;
});

console.log(nObj);