Learn JavaScript - Variables, Strings, Types
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Perform these exercises in the JavaScript console of your favorite web browser. What does the following expression return? 3 + 2;
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5
3 and 2 are called operands and + is the operator. |
What does the following expression return? typeof(3);
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"number"
There are a handful of data types in JavaScript (number, string, boolean, object, and undefined). Notice that there is only a single data type for numbers, not separate data types for integers and floating point numbers like some other languages. |
What does the following expression return? typeof(3) === typeof(4.32);
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true
3 is a "number" and 4.32 is a "number" as well, so the equality comparison of the types returns true. JavaScript has the same data type for integer and floating point numbers. |
What does the following expression return? 5 / 0;
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Infinity
Infinity is a very large number in JavaScript that is bigger than the biggest number JavaScript can represent. Technically, division by zero should return undefined, but this is a JavaScript quirk. |
What does the following expression return? 3 / "bob";
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NaN
NaN stands for "not a number" and is returned when a mathematical operation cannot yield a numeric result. |
What does the following expression return? NaN === NaN;
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false
NaN is not equal to any other value, including itself. |
What does the following expression return? typeof(NaN);
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"number"
NaN has a "number" type. |
What does the following expression return? isNaN(NaN);
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true
The isNaN method returns false if the argument is a number and true otherwise. isNaN returns true if the argument is NaN. |
What does the following expression return? Math.pow(2, 3);
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8
This expression represents 2 raised to the power of 3. The Math object contains methods to assist with common mathematical operations. |
Describe how the following expression assigns a variable to a value. var first_name = "cindy";
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The var keyword is used to declare a variable. In this case the var keyword declares the variable first_name. Additionally, this expression assigns the variable to the value "cindy". |
What is the value of the hello variable in the following expression? var hello;
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undefined
When a keyword is declared, but not assigned to any value, its value is undefined. |
What does the following expression return? var y;
y === "cool";
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false
The variable y has been declared, but it has not been assigned to anything, so its value is undefined. When undefined is compared with the string "cool" with the === equality operator, the return value is false. |
What does the following expression return? "some" + " person";
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"some person"
"some" and "person" are the operands and + is the operator. When the operands are strings, the + operator performs string concatenation. |
What does the following expression return? > var first = "Bart";
> var last = "Simpson";
> first + " " + last
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"Bart Simpson"
In this example, three strings are concatenated. |
What does the following expression return? "cool".length;
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4
The length property of strings returns the number of characters in a string. |
What does the following expression return? Explain the answer. "phat" === "phat";
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true
The === operator considers two strings equal if they both have the same length and the same characters in the same order. |
What does the following expression return? typeof("cats");
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"string"
"string" is one of the fundamental types in the JavaScript language. The other fundamental types are numbers, booleans, objects, and undefined. |
What does the following expression return? 3 + "bob"
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"3bob"
JavaScript cannot add a number and a string without converting the number to a string first. JavaScript converts 3 to "3" and then concatenates the two strings. 3 can be converted to "3" with this code: String(3); |
Round the number 4.87 to the nearest integer. |
Math.round(4.87);
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Divide the number 6 by the string "2" and explain the result. |
6 / "2" // returns 3
JavaScript cannot divide a number by a string, so it first converts the string to a number, and then performs the division. The string "2" can be converted to a number with this code Number("2"); Many programming languages raise exceptions for type mismatches, but JavaScript aggressively converts types instead. |
What does the following expression return? Explain the result. 3 * "bob";
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NaN
JavaScript attempts to convert "bob" to a number so multiplication can be performed, but the string "bob" cannot be converted to a number. Number("bob") returns NaN. 3 multiplied by NaN also returns NaN. |
Declare the variables x and y. |
var x, y;
// OR
var x;
var y;
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Set the variable hobby to the string "programming". |
var hobby = "programming";
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What does the following expression return? var sport;
sport === undefined
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true
A variable that has been declared, but has not been assigned to any value equals undefined. |
Demonstrate that "brogrammer" has the type "string". |
typeof("brogrammer");
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