💾isPrimitive()

check if value is a primitive

JS ⟩ values ⟩ custom functions ⟩ isPrimitive()

check if value is a primitive.

🗺️ 圖表

• replit：isPrimitive()

┌── (primitive ?)
│  typeof       type         expr         value       
---------------------------------------------------------------------
✅ object       Null         null         null
---------------------------------------------------------------------
✅ undefined    Undefined    undefined    undefined
---------------------------------------------------------------------
✅ number       Number       37           37
✅ number       Number       3.14         3.14
✅ number       Number       Math.LN2     0.6931471805599453
✅ number       Number       Infinity     Infinity ⭐️
✅ number       Number       NaN          NaN ⭐️
✅ number       Number       Number('1')  1
✅ number       Number       Number('ab') NaN
---------------------------------------------------------------------
✅ bigint       BigInt       42           42n
---------------------------------------------------------------------
✅ string       String       'bla'        'bla'
✅ string       String       `x = ${1+2}` 'x = 3'
✅ string       String       typeof 1     'number'
✅ string       String       String({})   '[object Object]'
✅ string       String       typeof xxx   'undefined'
---------------------------------------------------------------------
✅ boolean      Boolean      true         true
✅ boolean      Boolean      Boolean(1)   true
✅ boolean      Boolean      !!(1)        true
---------------------------------------------------------------------
✅ symbol       Symbol       Symbol()     Symbol()
✅ symbol       Symbol       Symbol.iterator Symbol(Symbol.iterator)
---------------------------------------------------------------------
❌ object       Object       {a:1}        { a: 1 }
❌ object       User         user         User { name: 'JohnDoe' }
❌ object       Array        [1, 2]       [ 1, 2 ]
❌ object       Date         new Date()   2022-09-13T01:47:46.344Z
❌ object       RegExp       /regex/      /regex/
---------------------------------------------------------------------
❌ function     Function     function(){} [Function (anonymous)]
❌ function     Function     Math.sin     [Function: sin]
❌ function     Function     () => {}     [Function (anonymous)]
❌ function     class        class {}     [class (anonymous)]
❌ function     class        User         [class User]
❌ function     GeneratorFunction function*(){} [GeneratorFunction (anonymous)]
---------------------------------------------------------------------

💾 程式

• replit：isPrimitive()

// ⭐ check if value is object
function isObject(value) {
    return value === Object(value)
}

// ⭐ check if value is primitive
function isPrimitive(value) {
    return !isObject(value)
}

// export
module.exports = { isObject, isPrimitive };

⭐️ 重點

Infinity, NaN are primitives.

The Object constructor's behavior depends on the input's type, if the value is

• null or undefined：empty object is returned.

• an object already：the value itself is returned.

• otherwise：object of a Type that corresponds to the value is returned.

Object(value) is identically to new Object(value)

👥 相關

• isObject() - check if value is an object.

💈範例

• replit：isPrimitive()

• require：test cases from typeName()

// ⭐ import (functions for type name)
const { typeName, baseTypeName } = require('./typeNames.js');
const { testCases } = require('./testCases.js');
const { isPrimitive } = require('./isPrimitive.js');

// table settings
const header = ['typeof', 'type', 'expr', 'value'];
const cols = header.length;
const [width, pad, ext] = [12, 1, 18];
const line = '-'.repeat(width*cols + pad*(cols-1) + ext);

// header
console.log('  ', ...header.map(s => s.padEnd(width, ' ')));
console.log(line);

// rows
for (const testCase of testCases) {

    // separator
    if (testCase === '---') {
        console.log(line); 
        continue; 
    }
    
    // test cases
    const value = testCase[0];
    const expr = testCase[1] || String(testCase[0]);

    const types = [typeof value, typeName(value)];
    const numberOfDifferentTypes = new Set(types.map(s => s.toLowerCase())).size;

    console.log(
         isPrimitive(value) ? '✅' : '❌',
        ...[...types, expr].map(s => s.padEnd(width, ' ')),
        value,
    )
}

console.log(line);

// legend
console.log(`• ⭐️ types not all the same        • ❗ base !== type`);

📘 手冊

• Object

⬇️ 應用

• printPrototypeChain() - print the prototype chain of an object.

🗣 討論

• Check if a value is an object in JavaScript

• test if a variable is a primitive rather than an object?