💾isClass()

JS ⟩ values ⟩ custom functions ⟩ isClass()

check if value is a class. (Note：class is also a Function)

replit：typeName() (v.2)
require： isFunction(), functionDefinition()
(to use it, copy and paste from 📁 module file： typeName())

// ⭐️ check if value is a "class"
// - require: 
//   • isFunction()
//   • functionDefinition()
function isClass(value) {
    return (
        // `value` is a function
        isFunction(value) &&
        // `value` is a "class" definition
        functionDefinition(value).startsWith("class")
    );
}

replit：isClass()
require： isFunction(), functionDefinition()

// normal function
function foo() {
    console.log('hello');
}

let a = 1;               // number
class User {}            // class
let user = new User();   // instance

// test cases
isClass(foo),    // ❌ false
isClass(a),      // ❌ false

isClass(User),   // ✅ true
isClass(user),   // ❌ false

// built-in objects
isClass(Object),        // ❌ false❗ 
isClass(Array),         // ❌ false❗ 
isClass(Promise),       // ❌ false❗
isClass(Proxy),         // ❌ false❗

isFunction(Object),     // ✅ true
isFunction(Array),      // ✅ true

// functionDefinition(a),   // ⛔ TypeError

functionDefinition(foo),    // function foo() {
                            //     console.log('hello');
                            // }
functionDefinition(Array),
// function Array() { [native code] }

functionDefinition(Promise),
// function Promise() { [native code] }

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Last updated 3 years ago

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