CoreJS: Booleans, Truthiness, and Conditionals

Boolean operators Part 1: Boolean Logic

Consider the following pieces of code and calculate by hand what value they should calculate, then check your results by entering them into the console.

1. true || false
2. ((true || false) && false) || true
3. var x; (x < 10) || (x > 10);
4. !!false
5. !((x >= 0) && (x <= 10)) === (!(x >= 0) || !(x <= 10))
6. !((x >= 0) && (x <= 10)) === ((x < 0) || (x > 10))
7. var x=1, y=1; x === y === 1;
8. var x = 0; -1 < x < 1

Boolean Operators Part 2: Non-Boolean values and Truthiness

1. 'coffee' || 'tea'
2. 'coffee' && 'tea'
3. 2 && 1 && 0
4. 2*Infinity && 'beyond'
5. undefined || false
6. undefined || undefined
7. 'banana'/2 || 'false'
8. var x, y=1; x || y;
9. var x = 0; (x === 1 || 2)

Conditionals

Consider the following fragments of code: execute them by hand, as shown in class, and then compare your answers to what you get from running the examples in scratchpad.

1.

var x;
if (x || (x=10)) {
    console.log(x);
} else {
    if (x && (+"totes a string")){
        console.log("one thing");
    } else {
        console.log("another thing");
    }
}

2.

if (x || !x) {
    console.log("We've excluded the middle");
} else {
    console.log("The middle is not excluded");
}

Boolean Operators Part 3: Short-circuting

Consider the following fragments of code and try to follow the logic of their execution and their outcome:

1. true || arglebarg
2. if (doJShomework() || runMarathon()) deserveCookie();
3. if (doJShomework() && runMarathon()) deserveCookie();
4. (backup = '') && deleteAllFiles()
5. treat() || trick()
6. practice() && win() && celebrate()

Summary

Summarize the following ideas in your own words:

• if-statements
• branching
• booleans
• truthiness
• short-circuiting

After you're done, share your answers within your group and discuss them.

Samples

console