javascriptoperatorslogical-operators

Javascript Logical Operator && used to Assign Properties

I encountered this piece of code:

var value = this.newTodo && this.newTodo.trim();

In this example: http://codepen.io/anon/pen/rONEMQ?editors=101

I don't understand what the AND (&&) operator is trying to accomplish.

In my understanding the && Operator is to asign multiple properties to a value, but this doesn't seem to be the case here.

I my code example, I don't see any difference, for when I use this:

var value = this.newTodo && this.newTodo.trim();

Instead of this:

var value = this.newTodo;

Or just this: 

var value = this.newTodo.trim();

Can anyone explain, what the initial line stated above and in the example does with the &&?

Solution 
  • var value = this.newTodo && this.newTodo.trim();

    if this.newTodo is not one of "falsey" values, i.e. "", 0, false, undefined, null, [] (I'm sure I'm forgetting some), then value = this.newTodo.trim(), otherwise value = this.newTodo (which could be "", 0, false, undefined, null, [] etc)

    I my code example, I don't see any difference, for when I use this:

    var value = this.newTodo && this.newTodo.trim();

    Instead of this:

    var value = this.newTodo;

    if this.newTodo is "Hello World" ... you're right, there is no difference

    if this.newTodo id " Hello World " ... value will be "Hello World" ... i.e. trimmed of leading and trailing spaces