JavaScript Conditional Statements

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Conditional statements

If else

if (everydayPack.lidOpen) {
 console.log("Lid is open!™);
} else {
 console.log("Lid is closed :(");
}

Ternary Operator

The conditional (ternary) operator is the only JavaScript operator that takes three operands: a condition followed by a question mark (?), then an expression to execute if the condition is truthy followed by a colon (:), and finally the expression to execute if the condition is falsy. This operator is frequently used as a shortcut for the if statement. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

// condition ? exprIfTrue : exprIfFalse
everydayPack.lidOpen ? "open" : "closed";
 
var age = 26;
var beverage = age >= 21 ? "Beer" : "Juice";
console.log(beverage); // "Beer"
 
// Handling null values
// One common usage is to handle a value that may be null
let greeting = person => {
  let name = person ? person.name : `stranger`;
  return `Howdy, ${name}`;
};
console.log(greeting({ name: `Alice` })); // "Howdy, Alice"
console.log(greeting(null)); // "Howdy, stranger"

Conditional chains

The ternary operator is right-associative, which means it can be “chained” in the following way, similar to an if … else if … else if … else chain:

function example(…) {
    return condition1 ? value1
         : condition2 ? value2
         : condition3 ? value3
         : value4;
}
 
// Equivalent to:
function example(…) {
    if (condition1) { return value1; }
    else if (condition2) { return value2; }
    else if (condition3) { return value3; }
    else { return value4; }
}