Joe Wood Notes

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Conditional

function checkNumber(num: number): string {
    if (num > 0) {
        return "Positive";
    } else if (num < 0) {
        return "Negative";
    } else {
        return "Zero";
    }
}

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Ternary and Select Expressions

Ternary operator:

const result = num > 0 ? "Positive" : num < 0 ? "Negative" : "Zero";

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Loop Over

TypeScript supports multiple loop constructs.

Basic for loop:

for (let i = 0; i < 5; i++) {
    console.log(i);
}

for...of (iterates over iterable objects):

const numbers: number[] = [1, 2, 3];
for (const num of numbers) {
    console.log(num);
}

for...in (iterates over object keys):

const user = { id: 1, name: "Alice" };
for (const key in user) {
    console.log(`${key}: ${user[key as keyof typeof user]}`);
}

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Loop Conditional Exit

TypeScript allows breaking out of loops based on conditions and also supports do...while loops, which execute at least once before checking the condition.

Basic do...while loop:

do {
    console.log("Executing at least once");
} while (false);

do...while with condition:

let i = 0;
do {
    console.log(i);
    i++;
} while (i < 5);
``` breaking out of loops based on conditions.

```typescript
for (let i = 0; i < 10; i++) {
    if (i === 5) {
        break; // Exit loop when i equals 5
    }
    console.log(i);
}

Using continue to skip iterations:

for (let i = 0; i < 10; i++) {
    if (i % 2 === 0) {
        continue; // Skip even numbers
    }
    console.log(i);
}

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Coroutine and Yield

TypeScript does not support native coroutines or yield, but it supports generator functions which behave similarly.

Generator function with yield:

function* numberGenerator(): Generator<number> {
    yield 1;
    yield 2;
    yield 3;
}

const gen = numberGenerator();
console.log(gen.next().value); // 1
console.log(gen.next().value); // 2
console.log(gen.next().value); // 3

Using yield in a loop:

function* infiniteCounter(): Generator<number> {
    let i = 0;
    while (true) {
        yield i++;
    }
}

const counter = infiniteCounter();
console.log(counter.next().value); // 0
console.log(counter.next().value); // 1
console.log(counter.next().value); // 2

Generators provide a way to implement lazy iteration, similar to coroutines in other languages.