Javascript: control flow

Conditions

To execute some block of code depending on a condition, the following constructions are used; they are exactly like in C programming language.

Simple if:

let x = 7;

if (x > 5) {
    console.log("x is greater than five");
}

x is greater than five

Construction if-else:

x = 3;

if (x > 5) {
    console.log("x is greater than five");
} else {
    console.log("x is not greater than five");
}

x is not greater than five

And the conditions can be chained together:

if (x > 10) {
    // Execute this if x > 10.
} else if (x > 5) {
    // Execute this if x > 5 but x <= 10.
} else if (x > 3) {
    // Execute this if x > 3 but x <= 3.
} else {
    // Execute this if x <= 3.
}

While loop

While loop is the most fundamental type of loop used in programming languages:

let i = 0;
while (i < 3) {
    console.log(i);
    i++;
}

For loop

Loops, where there is a counter variable that usually increments by one on each iteration, are pretty common in programming. As other C-family languages, Javascript offers for loop for such situations:

for (let i = 0; i < 5; i++) {
    let s = "";
    for (let j = 0; j < i+1; j++) {
        s += "*";
    }
    console.log(s);
}

*
**
***
****
*****

Note that there are two loops here—one is embedded in another. Moreover, the variable j of the inner loop is upper bounded by the variable i of the outer loop.

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