Section 3: Types and Operators

Question 1

Dynamic typing

Answer 1

You don’t tell the javascript engine what type of data a variable holds, the engine figures it out while your code is running/executing.

Variables can hold different types of values because it’s all figured out during execution. (“figuring things out on the fly”)

Question 2

Static typing

Answer 2

You tell the engine/compiler ahead of time what kind of data you intend to hold inside of a variable.

This is NOT what the javascript engine does. Javascript is dynamically typed, there is no keyword that tells the engine what kind of data you intend to put inside of the variable.

Question 3

Primitive type

Answer 3

A type of data that represents a single value. That is, not an object.

Question 4

undefined

Answer 4

A primitive type. undefined represents lack of existence (you shouldn’t set a variable to this)

Question 5

null

Answer 5

A primitive type. null represents lack of existence (you CAN set a variable to this…leave undefined to the javascript engine)

Question 6

boolean

Answer 6

A primitive type. true or false

Question 7

number

Answer 7

A primitive type. This is the only numeric type in javascript and it is a floating point number (there’s always some decimals).

Unlike other programming languages, there’s only one ‘number’ type… and it can make math weird.

Question 8

string

Answer 8

A primitive type. A sequence of characters (both ‘’ and “” can be used)

Question 9

symbol

Answer 9

A primitive type. Used in ES6 (next version of Javascript). Not fully supported as of Q4 2015.

Question 10

operator

Answer 10

A special function that is syntactically (written) differently.

Generally, operators take TWO parameters and return ONE result.

Question 11

infix notation

Answer 11

operator sits between two parameters (as opposed to prefix notation)

Question 12

Operator Precedence

Answer 12

Which operator function gets called first.

Functions are called in order of precedence (HIGHER precedence wins.)

Question 13

[Operator] Associativity

Answer 13

What order operator functions get called in: left-to-right OR right-to-left.

Note: When functions have the SAME PRECEDENCE

Question 14

var a = 2, b = 3, c = 4;
a = b = c;
console.log(a);
console.log(b);
console.log(c);

What is logged in the console?

Answer 14

4
4
4

Assignment operator (=) has a precedence of 3 and its associativity is right-to-left (aka right associative)

Question 15

Coercion

Answer 15

Converting a value from one type to another.

This happens quite often in Javascript because it’s dynamically typed.

var a = 1 + ‘2’; returns string ‘12’ because 1 is coerced into being a string representation of integer 1.

Question 16

What does Number(undefined) return?

Answer 16

NaN

Question 17

What does Number(null) return?

Answer 17

0

Question 18

True or False: null coerces to 0 for comparison ( == )

Answer 18

False. Null does not coerce to 0 for comparison.

Question 19

True or false:

Does strict equality ( === ) coerce values?

Answer 19

False. Strict equality does not coerce values in the way that equality ( == ) will.

Question 20

In an if() statement, what is the javascript engine trying to convert the condition in parens to?

Answer 20

A boolean (true or false)

Question 21

What does the following return?

false || true

Answer 21

True

Question 22

What does this return when the function greet() is called?

function greet(name) { console.log('Hello ' + name); }
greet();

Answer 22

Hello undefined

Question 23

What does this return:

function greet(name) { name = name || ‘; console.log(‘Hello ‘ + name; }

greet(‘Tony’);
greet(0);
greet();

Answer 23

Hello Tony
Hello
Hello

Question 24

What is this code doing?

window.libraryName = window.libraryName || “Lib 2”;

Answer 24

It’s checking the window object - the global execution context/object - for any variable already named libraryName and if not, using the || operator, var libraryName is being give the value “Lib 2”