Conditionally Add Member to Object Javascript

ES6 Code:

Object.assign(a, conditionB ? { b: 1 } : null,
                 conditionC ? { c: 2 } : null,
                 conditionD ? { d: 3 } : null);

Sugar ES6 Code:

const a = {
   ...(someCondition && {b: 5})
}

Above works as : spread operator is like a shorthand of Object.assign and have lower precedence than the && operator. It ignore value without property (boolean, null, undefined, number), and add all properties of the object after the … in place. remember the && operator return the right value if true, or false otherwise. So if someCondition is true, {b : 5} will be passed to the … operator, resulting in adding the property b to a with value 5. If someCondition is false, false will be passed to the … operator. resulting in nothing added.