Types & Truthiness

Type matchers

Type matchers confirm the compile-time type of the expression. They resolve during compilation, so they are effectively free at runtime.

expect("hello").toBeString();
expect(true).toBeBoolean();
expect([1, 2, 3]).toBeArray();
expect(42).toBeNumber();

Matcher	Passes when the value is
toBeString()	a string
toBeBoolean()	a boolean
toBeArray()	an array
toBeNumber()	an integer or float (see Numbers)

Truthiness

toBeTruthy and toBeFalsy apply AssemblyScript's truthiness rules to any value:

expect(1).toBeTruthy();
expect("non-empty").toBeTruthy();
expect(0).toBeFalsy();
expect("").toBeFalsy();
expect(<string | null>null).toBeFalsy();

Value	Truthy?
non-zero number	yes
0, NaN	no
non-empty string	yes
empty string	no
non-null reference	yes
null	no
true / false	as written

Combine with .not when an explicit negative reads better than a toBeFalsy:

expect(handle).not.toBeNull();
expect(items.length).toBeTruthy();