Logical Operators: And

Sometimes one condition isn't enough. “If it's Friday and it's warmer than 20 °C, I'll go out” is made of two conditions joined by the word “and”. In JavaScript, “and” is written &&:

const day = "Friday";
const temperature = 25;
if (day === "Friday" && temperature > 20) {
    console.log("I'm going out");
}

This prints:

I'm going out

&& is a logical operator: it joins two conditions into one. The joined condition is true only if both parts are true. If even one of them is false, the whole condition is false:

• true && true is true
• true && false is false
• false && true is false
• false && false is false

You can join more conditions in a row: a && b && c is true only if all three are true.

Each part must be a complete comparison. “Age from 13 to 19” is age >= 13 && age <= 19. If you write age >= 13 && <= 19, the program ends with SyntaxError: Unexpected token '<='. And 13 <= age <= 19, as in math, runs without an error but gives wrong results (it's true even for an age of 25), because JavaScript compares only two values at a time.