Merge multiple objects inside the same array into one object

If your environment supports Object.assign, then you can do the same in a succinct way like this

const arrObj = [{a: 1, b: 2}, {c: 3, d: 4}, {e: 5, f: 6}];

console.log(arrObj.reduce(function(result, current) {
  return Object.assign(result, current);
}, {}));

// If you prefer arrow functions, you can make it a one-liner ;-)
console.log(arrObj.reduce(((r, c) => Object.assign(r, c)), {}));

// Thanks Spen from the comments. You can use the spread operator with assign
console.log(Object.assign({}, ...arrObj));

ES5 solution:

You can use Array.prototype.reduce like this

var resultObject = arrObj.reduce(function(result, currentObject) {
    for(var key in currentObject) {
        if (currentObject.hasOwnProperty(key)) {
            result[key] = currentObject[key];
        }
    }
    return result;
}, {});

console.log(resultObject);
# { a: 1, b: 2, c: 3, d: 4, e: 5, f: 6 }

This solution, simply gathers all the keys and their values in every object in the result, which is finally returned to us as the result.

This check

if (currentObject.hasOwnProperty(key)) {

is necessary to make sure that we are not including all the inherited enumerable properties in the result.

You could use reduce for an elegant solution:

arrObj.reduce(function(acc, x) {
    for (var key in x) acc[key] = x[key];
    return acc;
}, {});

See MDN docs for reduce for more information.