Javascript Difference Between x=10; if(x) and if(x===10)

Question

I understand that in terms of boolean

x = true; if(x) //This is the same as if(x === True) doSomething();

But if one were to set x to a number, then what does the if condition mean? Does the condition mean if(x === true)? If so, why is that?

Answer 1

In javascript the below are falsey

• false
• undefined
• null
• 0
• ""
• NaN

Anything except the above are truthy, including numbers, except 0. So 10 is a truthy value and hence the if block, executes.

Answer 2

in short is as follows:

//!length = if(x.length);
var a;                                      //undefined == if(!a) == !length
var b = "";                                 //void  == if(!b)
var c = " ";                                //blank == if(c) == length
var d = "text";                             //there == if(d) == length
var e = true;                               //true == true == if(e)
var f = false;                              //false == false == if(!f)
var g = null;                               //false == if(!g) == !length
var h = 0;                                  //0 == if(!h)
var i = 1;                                  //true == if(i)
var j = 0/0;                                //NaN == if(!j)
var k = document.body;                      // == if(k)
var l = document.getElementById("nothing"); // if(!l) == !length

Javascript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:

if(!blah){

Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN

var a;           //undefined == if(!a) == !length
var b = "";      //void  == if(!b)
var c = " ";     //blank == if(c) == length
var d = "text";  //there == if(d) == length
var e = true;    //true == true == if(e)
var f = false;   //false == false == if(!f)
var g = null;    //false == if(!g) == !length
var h = 0;       //0 == if(!h)
var i = 1;       //true == if(i)
var j = 0/0;     //NaN == if(!j)
var k = document.body; // == if(k)
var l = document.getElementById("nothing"); // if(!l) == !length

consoletotal(l);

function consoletotal(bb){
    consolea(bb);
    consoleb(bb);
    consolec(bb);
    consoled(bb);
    consolee(bb);
}
function consolea(bb){
    if(bb){
        console.log("yes" + bb);
    }
}
function consoleb(bb){
    if(bb===true){
        console.log("true" + bb);
    }
}
function consolec(bb){
    if(bb===false){
        console.log("false" + bb);
    }
}
function consoled(bb){
    if(!bb){
        console.log("no" + bb);
    }
}
function consolee(bb){
    if(bb.length){
        console.log("length" + bb);
    }
}