Errors

When using the Assert function, an error will be thrown if the value provided does not conform to the specified type. The error thrown will be an instance of TError.

import { T, TError } from "type-guarder";
 
try {
  T.string().assert(123);
} catch (error) {
  if (error instanceof TError) {
    error.expectedType; // "string"
    error.actualType; // "number"
    error.value; // 123
    error.message; // "The type of `123` is `number` and it should be `string`";
  } else {
    throw error;
  }
}

When an error occurs in a nested type like within an array or object, the error will also contain a trace of the path to the value that failed the type check.

import { T, TError } from "type-guarder";
 
const checker = T.object({
  name: T.object({
    first: T.string(),
    last: T.string(),
  }),
  age: T.Integer(),
});
 
try {
  const { name, age } = checker.assert({
    name: {
      first: "John",
      last: false,
    },
    age: 123,
  });
  console.log(`Hello ${name.first} ${name.last}! You are ${age} years old.`);
} catch (error) {
  if (error instanceof TError) {
    error.expectedType; // "string"
    error.actualType; // "boolean"
    error.value; // false
    error.message; // "The type of `false` at `name.last` is `boolean` and it should be `string`";
  } else {
    throw error;
  }
}

Functions Boolean