Decisions and branching logic

There are a nuumber of mechanisms to evaluate criteria and choose what to do. // being that you dont want to assign a new value to your test variable, use the double == or tripple === as comparison operators,

• Decisions and branching logic
  • If-then-else
  • Switch statement
  • Ternary operator
  • Logical OR
  • Nulish coalesence
  • Optional Chaining

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If-then-else

If condition true do something else do something else

// prints 1
let myChoice = 1;
if (myChoice == 0){
    console.log("You chose 0");
}
else if (myChoice == 1){ 
    console.log("You chose 1");
}
else {
    console.log("You chose something weird");
};

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Switch statement

if condition matches an option do something specific else do a default operation

// switch - prints "You chose 1"
myChoice = 1
switch (myChoice) {
    case 0:
        console.log("You chose 0");
        break;
    case 1:
        console.log("You chose 1");
        break;
    default:
        console.log("You chose something weird");
        break;
}

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Ternary operator

If true do this, else that. (three parts) - condition ? true part : false part

let age = 19;
let text = (age < 18) ? "Minor" : "Adult";
console.log("Ternary: " + text);  // Will return 'Ternary: Adult'

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Logical OR

Return true bit or false bit. (returnedValue = thisIfTrue OR otherwiseThis)

let firstPort;
let secondPort = 9999;

let port = firstPort || 3000;
console.log(port); // defaults to 3000 as firstPort is not initialised

port = secondPort || 3000;
console.log(port); // uses 9999 as secondPort value initialised.

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Nulish coalesence

If a variable is null or undefined, return it, otherwise return something else. ( varToTest ?? returnThisIfFalse)

let r;
const q = "cat";

console.log( r ?? "dog"); // prints dog because r is null or undefined
console.log( q ?? "dog"); // prints cat as variable already initialised

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Optional Chaining

Return ‘undefined’ if a higher-level object is not present, rather than error. (?)

let person = {
    name: 'Fred',
    email: 'fred.flintstone@quarry.com'
}

console.log(person.avatar?.url);  // If avatar property undefined, dont get url, just return undefined

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