assert (function)

const assert: {
  <ValueType>(
    value: ValueType,
    message?: string,
  ): asserts value is ValueType extends null | undefined | false | 0 | ""
    ? never
    : ValueType;
  type: <T extends TypeValidator<any> | CoerceableToTypeValidator>(
    value: any,
    type: T,
    optionalMessage?: string,
  ) => asserts value is UnwrapTypeFromCoerceableOrValidator<T>;
};

assert(...) (call signature)

Throws an error if value is not truthy.

• @param value — The value to test for truthiness
• @param message — An optional error message to use. If unspecified, "Assertion failed" will be used.

Example

const files = ls();
assert(files.length > 0, "Expected the current directory to have files");

<ValueType>(value: ValueType, message?: string): asserts value is ValueType extends null | undefined | false | 0 | "" ? never : ValueType;

assert.type (function property)

Throws an error if its argument isn't the correct type.

• @param value — The value to test the type of
• @param type — The type that value should be, as either a TypeValidator (from the types.* namespace) or a value which can be coerced into a TypeValidator via the types.coerce function, like String, Boolean, etc.
• @param message — An optional error message to use. If unspecified, a generic-but-descriptive message will be used.

Example

const port: unknown = 8080;
assert.type(port, Number, "port must be a number");
console.log(port.toFixed(0));

type: <T extends TypeValidator<any> | CoerceableToTypeValidator>(value: any, type: T, optionalMessage?: string) => asserts value is UnwrapTypeFromCoerceableOrValidator<T>;