checker

This is a library of commonly used validation logic for Typescript.

Every function has an inverse, for example check_is_string and check_is_not_string.

Data type	Library
string	@checker/string
number	@checker/number
boolean	@checker/boolean
nullish	@checker/nullish
array	@checker/array
object	@checker/object

Examples:

• @checker/string

  import { check_is_string } from "@checker/string";
  
  type Value = string | null;
  
  let value: Value = null;
  
  if (someCondition) {
    value = "hello";
  }
  
  if (check_is_string(value)) {
    value; // value is Hello and this type is string
  }

  import { check_is_index_found } from "@checker/string";
  
  const words = "hello world";
  
  const index = words.indexOf("hello");
  
  if (check_is_index_found(index)) {
    // When index is not -1
  }

  import { check_is_empty_string } from "@checker/string";
  
  const value = "    ";
  const trimmed = value.trim();
  
  if (check_is_empty_string(trimmed)) {
    // When value is empty string
  }

• @checker/number

  import { check_is_number, check_is_odd } from "@checker/number";
  
  const array = ["a", 1, true, 2, 3, 4, 5];
  
  const odds = array.filter(check_is_number).filter(check_is_odd);
  // odds = [1, 3, 5]

• @checker/boolean

  import { check_is_truthy } from "@checker/boolean";
  
  const array = [null, undefined, 0, 1, , "", "hello", true];
  
  const filtered = array.filter(check_is_truthy); // [1, 'hello', true]

• @checker/nullish

  import { check_is_not_nullish } from "@checker/nullish";
  
  const array = [null, undefined, 0, 1, '', 'hello' true];
  
  const filtered = array.filter(check_is_not_nullish); // [0, 1, '', 'hello', true]

• @checker/array

  Checks if the given index is the last iteration in the array.

  import { check_is_last_iteration } from "@checker/array";
  
  const array = [1, 2, 3];
  
  const mapped = array.map((item, index) => {
    if (check_is_last_iteration(index, array)) {
      return item + 1;
    }
    return item;
  });
  // mapped = [1, 2, 4]

• @checker/object

  Checks if the given index is not the last iteration in the array.

  import { check_is_empty_object } from "@checker/object";
  
  type Value = Partial<{ [key: string]: boolean }>;
  
  const value: Value = {};
  
  if (someCondition) {
    value["key"] = true;
  }
  
  if (check_is_empty_object(value)) {
    // When value is empty object
  }

  import { check_is_instance } from "@checker/object";
  
  try {
    // some action
  } catch (err) {
    if (check_is_instance(err, DatabaseError)) {
      // err is DatabaseError instance
    }
  }

Licence

All library licence is MIT.