refactor(helper-functions): add isString and isNumber helper functions

- those helper functions also return true when a value was created using the constructor (new Number() or new String())
- refactor usage of typeof value to isString() or isNumber()

Author: michaelwittwer

src/dynamo/expression/param-util.ts

@@ -3,6 +3,7 @@
  */
 import * as DynamoDB from 'aws-sdk/clients/dynamodb'
 import { isEmpty } from '../../helper/is-empty.function'
+import { isString } from '../../helper/is-string.function'
 import { ConditionalParams } from '../operation-params.type'
 import { resolveAttributeValueNameConflicts } from './functions/resolve-attribute-value-name-conflicts.function'
 import { Expression } from './type/expression.type'
@@ -44,7 +45,7 @@ export function addExpression(
   }
 
   const statement = params[expressionType]
-  if (typeof statement === 'string' && statement !== '') {
+  if (isString(statement) && statement !== '') {
     switch (expressionType) {
       case 'UpdateExpression':
         ;(<any>params)[expressionType] = mergeUpdateExpressions(statement, nameSafeCondition.statement)

src/helper/get-tag.function.ts

@@ -0,0 +1,8 @@
+import { Tag } from './tag.enum'
+
+/**
+ * @return Returns the value (we call it tag) returned by function call `value.toString`,
+ */
+export function getTag(value: any): Tag | string {
+  return Object.prototype.toString.call(value)
+}

src/helper/is-number.function.ts

@@ -0,0 +1,9 @@
+import { getTag } from './get-tag.function'
+import { Tag } from './tag.enum'
+
+/**
+ * @return Returns true for any value where typeof equals 'number' or an object created with Number constructor
+ */
+export function isNumber(value: any): boolean {
+  return typeof value === 'number' || getTag(value) === Tag.NUMBER
+}

src/helper/is-number.spec.ts

@@ -0,0 +1,18 @@
+import { isNumber } from './is-number.function'
+
+describe('is number', () => {
+  it('should be a number', () => {
+    expect(isNumber(3)).toBeTruthy()
+    expect(isNumber(NaN)).toBeTruthy()
+    expect(isNumber(Infinity)).toBeTruthy()
+    // tslint:disable:no-construct
+    expect(isNumber(new Number('2'))).toBeTruthy()
+    expect(isNumber(new Number('myNumber'))).toBeTruthy()
+  })
+
+  it('should not be a number', () => {
+    expect(isNumber('a')).toBeFalsy()
+    expect(isNumber({})).toBeFalsy()
+    expect(isNumber([])).toBeFalsy()
+  })
+})

src/helper/is-plain-object.function.ts

@@ -1,11 +1,13 @@
 // https://github.com/jonschlinkert/is-plain-object
+import { getTag } from './get-tag.function'
+import { Tag } from './tag.enum'
 
 function isObject(val: any) {
   return val != null && typeof val === 'object' && Array.isArray(val) === false
 }
 
 function isObjectObject(o: any): boolean {
-  return isObject(o) === true && Object.prototype.toString.call(o) === '[object Object]'
+  return isObject(o) === true && getTag(o) === Tag.OBJECT
 }
 
 export function isPlainObject(o: any): boolean {

src/helper/is-string.function.ts

@@ -0,0 +1,9 @@
+import { getTag } from './get-tag.function'
+import { Tag } from './tag.enum'
+
+/**
+ * @return Returns true for any value where typeof equals 'string' or an object created with String constructor
+ */
+export function isString(value: any): boolean {
+  return typeof value === 'string' || getTag(value) === Tag.STRING
+}

src/helper/is-string.spec.ts

@@ -0,0 +1,17 @@
+import { isString } from './is-string.function'
+
+describe('is string', () => {
+  it('should be a string', () => {
+    expect(isString('myValue')).toBeTruthy()
+    // tslint:disable:no-construct
+    expect(isString(new String('2'))).toBeTruthy()
+    expect(isString(new String('someValue'))).toBeTruthy()
+  })
+
+  it('should not be a string', () => {
+    expect(isString(3)).toBeFalsy()
+    expect(isString(true)).toBeFalsy()
+    expect(isString({})).toBeFalsy()
+    expect(isString([])).toBeFalsy()
+  })
+})

src/helper/tag.enum.ts

@@ -0,0 +1,6 @@
+/** used to compare with value returned by @link getTag(value), this is not a complete list only the one values used are defined */
+export enum Tag {
+  OBJECT = '[object Object]',
+  STRING = '[object String]',
+  NUMBER = '[object Number]',
+}

src/mapper/for-type/number.mapper.ts

@@ -1,6 +1,7 @@
 /**
  * @module mapper
  */
+import { isNumber } from '../../helper/is-number.function'
 import { NumberAttribute } from '../type/attribute.type'
 import { MapperForType } from './base.mapper'
 
@@ -17,7 +18,7 @@ function numberFromDb(attributeValue: NumberAttribute): number {
 }
 
 function numberToDb(modelValue: number): NumberAttribute | null {
-  if (typeof modelValue !== 'number') {
+  if (!isNumber(modelValue)) {
     throw new Error(`this mapper only support values of type number, value given: ${JSON.stringify(modelValue)}`)
   }
 

src/mapper/util.ts

@@ -2,6 +2,8 @@
  * @module mapper
  */
 import { PropertyMetadata } from '../decorator/metadata/property-metadata.model'
+import { isNumber } from '../helper/is-number.function'
+import { isString } from '../helper/is-string.function'
 import { ModelConstructor } from '../model/model-constructor'
 import { AttributeCollectionType, AttributeType } from './type/attribute-type.type'
 import { AttributeValueType } from './type/attribute-value-type.type'
@@ -145,9 +147,9 @@ export function isSet(value: any): value is Set<any> {
  * @hidden
  */
 export function detectType(value: any): AttributeType {
-  if (typeof value === 'string') {
+  if (isString(value)) {
     return 'S'
-  } else if (typeof value === 'number') {
+  } else if (isNumber(value)) {
     return 'N'
   } else if (isBinary(value)) {
     return 'B'