What?

A javascript error generator that takes a function as input and creates test cases to show any errors that can be found

Uses

• Integration into an IDE or text editor.
• As part of a test suite or build process.

Similar tools

• Static analysers such as
• Hand coded tests.
• Code coverage tools.

Why?

Javascript

• Dynamic typing
• Type coercion
• Objects that act like hash maps
• Prototypal inheritance

Dynamic Typing

Variables can contain any type of value.

var a;
a = 1;  // number
a = ""; // string
a = {}; // object
a = []; // array
a = /^regular expression$/g; // regular expression
						

Dynamic Objects

• Objects act something like hashmaps.
• Properties can be added and removed

var a = {};
a.property = "a string";

function example(a) {
	// checking if a will have a certain property
	if(a.property != null) {
		// do something...
	}
}
						

Type Errors

TypeErrors are the most common type of error.

function example(callback) {
	//do something

	callback();
}
						

Possible Solution

function greeter(person: string) {
		return "Hello, " + person;
}

var user = "Jane User";

document.body.innerHTML = greeter(user);
						

Type Coercion

Values can be coerced to perform operations on different types.

"1" + 2 + 3 = "123"
"3" - 1 = 2
null == undefined
						

Symbolic Execution

Execution of a program using symbolic values rather than real ones.

Symbolic Execution - Problems

• Loops
• Path explosion
• Representation of multiple types
• Strings and Arrays

Example

function example(obj) {
	if(obj != null) {
		if(obj.prop == null) {
			obj.prop = {};
		}
		obj.prop.value = 10;
	}
}