How to get all properties of an object?

Question

How to get all properties of an object using reflection in JavaScript?

Answer 1

The JavaScript has no good, built-in tools for the reflection (introspection), so you need made it manually.

At first, here a code of a solution

/**
 * Display details about an object at run-time
 * @param  {[any]} target Any object
 * @return Nothing, all information will be display
 */
const introspect = (target) => {
    // get type of a target
    const typeTarget = typeof target;

    // variable for type attribute of the target
    let typeAttr;

    // for properties and methods of the target
    let properties = [];
    let methods = [];

    // if target is array, keep names all enumerable properties, simple put - numbers of indexes
    // otherwise set to null
    const enumerableProperties = Array.isArray(target) ? Object.keys(target) : null;

    // determination functions and properties of the target by a parent object
    Object.getOwnPropertyNames(Object.getPrototypeOf(target)).forEach((name) => {
        if (typeof target[name] === 'function') {
            methods.push(name);
        } else if (target.hasOwnProperty(name) && properties.indexOf(name) === -1) {
            properties.push(name);
        }
    });

    // determination other functions and properties of the target
    // filter it, if a name already added or if it is an array - filter all values of the indexes
    Object.getOwnPropertyNames(target).forEach((name) => {
        if (enumerableProperties !== null && enumerableProperties.indexOf(name) !== -1) {
            return;
        }
        if (typeof target[name] === 'function') {
            methods.push(name);
        } else if (target.hasOwnProperty(name) && properties.indexOf(name) === -1) {
            properties.push(name);
        }
    });

    // order properties and methods by name in reverse
    properties = properties.reverse();
    methods = methods.reverse();

    // display an obtained information by groups
    console.log(`${typeTarget}: "${target}"`);
    console.log(`\n\tProperties: ${properties.length}\n\t------------------`);
    for (let i = properties.length - 1; i >= 0; i -= 1) {
        typeAttr = typeof target[properties[i]];
        console.log(`\t\t${properties[i]} --> ${typeAttr}`);
    }

    console.log(`\n\tMethods: ${methods.length}\n\t------------------`);
    for (let i = methods.length - 1; i >= 0; i -= 1) {
        let args = functools.getFunctionParameters(target[methods[i]]);
        args = args.join(', ');
        console.log(`\t\t${methods[i]} (${args})`);
    }
};

Examine this function on real examples.

For built-in object Array

introspect(Array);

Result:

function: "function Array() { [native code] }"

    Properties: 5
    ------------------
        length --> number
        name --> string
        arguments --> object
        caller --> object
        prototype --> object

    Methods: 8
    ------------------
        apply ()
        bind ()
        call ()
        toString ()
        constructor ()
        isArray ()
        from ()
        of ()

For real array (instance of object Array)

introspect([-10, '20', true, []]);

Result:

object: "-10,20,true,"

    Properties: 1
    ------------------
        length --> number

    Methods: 29
    ------------------
        constructor ()
        toString ()
        toLocaleString ()
        join ()
        pop ()
        push ()
        reverse ()
        shift ()
        unshift ()
        slice ()
        splice ()
        sort ()
        filter ()
        forEach ()
        some ()
        every ()
        map ()
        indexOf ()
        lastIndexOf ()
        reduce ()
        reduceRight ()
        copyWithin ()
        find ()
        findIndex ()
        fill ()
        includes ()
        entries ()
        keys ()
        concat ()

What about a real object?

introspect({
    aa: 1,
    bb: true,
    cc: [],
    dd: {},
    c: (z, a= 2) => {},
    b: function(z   =  1, a=2) {},
    d: function(b, zzz) {},
});

Result:

object: "[object Object]"

    Properties: 4
    ------------------
        aa --> number
        bb --> boolean
        cc --> object
        dd --> object

    Methods: 14
    ------------------
        hasOwnProperty ()
        constructor ()
        toString ()
        toLocaleString ()
        valueOf ()
        isPrototypeOf ()
        propertyIsEnumerable ()
        __defineGetter__ ()
        __lookupGetter__ ()
        __defineSetter__ ()
        __lookupSetter__ ()
        c (z, a = 2)
        b (z = 1, a = 2)
        d (b, zzz)

This function also good work with the built-in modules. Make introspect the module Math.

introspect(Math);

Result

object: "[object Math]"

    Properties: 8
    ------------------
        E --> number
        LN10 --> number
        LN2 --> number
        LOG2E --> number
        LOG10E --> number
        PI --> number
        SQRT1_2 --> number
        SQRT2 --> number

    Methods: 46
    ------------------
        hasOwnProperty ()
        constructor ()
        toString ()
        toLocaleString ()
        valueOf ()
        isPrototypeOf ()
        propertyIsEnumerable ()
        __defineGetter__ ()
        __lookupGetter__ ()
        __defineSetter__ ()
        __lookupSetter__ ()
        acos ()
        asin ()
        atan ()
        ceil ()
        clz32 ()
        floor ()
        fround ()
        imul ()
        max ()
        min ()
        round ()
        sqrt ()
        trunc ()
        random ()
        abs ()
        exp ()
        log ()
        atan2 ()
        pow ()
        sign ()
        asinh ()
        acosh ()
        atanh ()
        hypot ()
        cbrt ()
        cos ()
        sin ()
        tan ()
        sinh ()
        cosh ()
        tanh ()
        log10 ()
        log2 ()
        log1p ()
        expm1 ()

Matter what pollute answer superfluous code, try do it yourself and see results

introspect(34.2313);
introspect(true);
introspect(Date);
introspect((new Date()));
introspect(String);
introspect('text');

For full code, I also show the function "getFunctionParameters" (in module "functools.js"), since it used it.

/**
 * Return array paraments of a function
 * @param  {[function]} func function
 * @return {[array]}      parameters the functions
 *
 */
const getFunctionParameters = (func) => {
    if (typeof func !== 'function') {
        throw new Error('A argument is not function.');
    }
    const args = func.toString().match(/\((.*)\)/)[1];
    return args.split(',').map((arg) => {
        if (arg.indexOf('=') === -1) return arg.trim();
        return arg
            .split('=')
            .map(val => val.trim())
            .join(' = ');
    });
};

Notes:

1. Weakly tested

2. Full code here https://github.com/setivolkylany/nodejs-utils

3. Good resource about it topic http://www.2ality.com/2011/01/reflection-and-meta-programming-in.html

4. Used the features of the ES6

Answer 2

In modern browsers, to get all property names (not just enumerable properties), you'd use Object.getOwnPropertyNames...

var props = Object.getOwnPropertyNames(my_object)

If you don't want enumerable properties, you'd use Object.keys...

var props = Object.keys(my_object)

Answer 3

var point = { x:5, y:8 };

for( var name in point ) {
    // name contains the property name that you want
    // point[name] contains the value
}

Answer 4

Loop through the object and take every key that belongs to it and is not a function:

var properties = [];
for(var key in obj) {
    if(obj.hasOwnProperty(key) && typeof obj[key] !== 'function') {
        properties.push(key);
    }
}