Operators and flows

JavaScript supports similar control structures to other languages in the C family. Conditional statements are written with if and else, and you can chain together the statements using else-if ladders.

var a = "some value"; 
if(a === "other value") { 
  //do something 
} else if (a === "another value") { 
  //do something 
} else { 
  //do something 
} 

Control statements can be written using while, do-while, for, and switch statements. One important thing to consider while writing conditions in JavaScript is to understand what equates to true and/or false. Any value greater or less than zero, not null, and not undefined equates to true. Strings such as 0, null, undefined, or empty strings equate to false.

Some sample examples using while, do-while, for, and switch statements are as follows:

// for loop example 
 
var myVar = 0; 
for(let i = 0; i < 100; i += 1) {  
  myVar = i; 
  console.log(myVar); // => 0 1 ... 99 
} 
 
// do while example 
var x = 0; 
do { 
  x += 1; 
  console.log(x); // => 1 2 ... 100 
} while (x < 100); 
 
// while example 
while (x > 90) { 
  x -= 1; 
  console.log(x); // => 99 98 ... 90 
} 
//switch example 
 
var x = 0; 
switch(x) { 
  case 1 :  
console.log(""one""); 
break; 
  case 2 :  
console.log("two""); 
break; 
  default: 
console.log("none"); 
 
} // => "none" 

Another important thing will be to understand the basic difference between
the comparisons using == and ===. The == comparisons should be used where
the type of variable is not your concern; and if the data type of the variables also should be compared, then you should opt for a === comparison symbol as given in the following code:

const a = '5'; 
const b = 5; 
if(a == b) { 
  //do something 
} 
if(a === b) { 
  //do something 
} 

Here in the code snippet, the first condition evaluates to true while the second doesn't. So while you code, it's always safer to depend on strict (===) equality checks as a best practice.