Is there an equivalent for var_dump (PHP) in Javascript?

As the others said, you can use Firebug, and that will sort you out no worries on Firefox. Chrome & Safari both have a built-in developer console which has an almost identical interface to Firebug's console, so your code should be portable across those browsers. For other browsers, there's Firebug Lite.

If Firebug isn't an option for you, then try this simple script:

function dump(obj) {
    var out = '';
    for (var i in obj) {
        out += i + ": " + obj[i] + "\n";
    }

    alert(out);

    // or, if you wanted to avoid alerts...

    var pre = document.createElement('pre');
    pre.innerHTML = out;
    document.body.appendChild(pre)
}

I'd recommend against alerting each individual property: some objects have a LOT of properties and you'll be there all day clicking "OK", "OK", "OK", "O... dammit that was the property I was looking for".

If you are using firefox then the firebug plug-in console is an excellent way of examining objects

console.debug(myObject);

Alternatively you can loop through the properties (including methods) like this:

for (property in object) {
    // do what you want with property, object[property].value
}

It can't be stated enough that you can use console.debug(object) for this. This technique will save you literally hundreds of hours a year if you do this for a living :p

If you use Firebug, you can use console.log to output an object and get a hyperlinked, explorable item in the console.

I improved nickf's answer, so it recursively loops through objects:

function var_dump(obj, element)
{
    var logMsg = objToString(obj, 0);
    if (element) // set innerHTML to logMsg
    {
        var pre = document.createElement('pre');
        pre.innerHTML = logMsg;
        element.innerHTML = '';
        element.appendChild(pre);
    }
    else // write logMsg to the console
    {
        console.log(logMsg);
    }
}

function objToString(obj, level)
{
    var out = '';
    for (var i in obj)
    {
        for (loop = level; loop > 0; loop--)
        {
            out += "    ";
        }
        if (obj[i] instanceof Object)
        {
            out += i + " (Object):\n";
            out += objToString(obj[i], level + 1);
        }
        else
        {
            out += i + ": " + obj[i] + "\n";
        }
    }
    return out;
}

You can simply use the NPM package var_dump

npm install var_dump --save-dev

Usage:

const var_dump = require('var_dump')

var variable = {
  'data': {
    'users': {
      'id': 12,
      'friends': [{
        'id': 1,
        'name': 'John Doe'
      }]
    }
  }
}

// print the variable using var_dump
var_dump(variable)

This will print:

object(1) {
    ["data"] => object(1) {
        ["users"] => object(2) {
            ["id"] => number(12)
            ["friends"] => array(1) {
                [0] => object(2) {
                    ["id"] => number(1)
                    ["name"] => string(8) "John Doe"
                }
            }
        }
    }
}

Link: https://www.npmjs.com/package/@smartankur4u/vardump

Thank me later!

Here is my solution. It replicates the behavior of var_dump well, and allows for nested objects/arrays. Note that it does not support multiple arguments.

function var_dump(variable) {
  let out = "";
  
  let type = typeof variable;
  if(type == "object") {
    var realType;
    var length;
    if(variable instanceof Array) {
      realType = "array";
      length = variable.length;
    } else {
      realType = "object";
      length = Object.keys(variable).length;
    }
    out = `${realType}(${length}) {`;
      for (const [key, value] of Object.entries(variable)) {
    out += `\n [${key}]=>\n ${var_dump(value).replace(/\n/g, "\n  ")}\n`;
  }
  out += "}";
  } else if(type == "string") {
    out = `${type}(${type.length}) "${variable}"`;
  } else {
    out = `${type}(${variable.toString()})`;
  }
  return out;
}
console.log(var_dump(1.5));
console.log(var_dump("Hello!"));
console.log(var_dump([]));
console.log(var_dump([1,2,3,[1,2]]));

console.log(var_dump({"a":"b"}));

Late to the game, but here's a really handy function that is super simple to use, allows you to pass as many arguments as you like, of any type, and will display the object contents in the browser console window as though you called console.log from JavaScript - but from PHP

Note, you can use tags as well by passing 'TAG-YourTag' and it will be applied until another tag is read, for example, 'TAG-YourNextTag'

/*
*   Brief:          Print to console.log() from PHP
*   Description:    Print as many strings,arrays, objects, and other data types to console.log from PHP.
*                   To use, just call consoleLog($data1, $data2, ... $dataN) and each dataI will be sent to console.log - note that
*                   you can pass as many data as you want an this will still work.
*
*                   This is very powerful as it shows the entire contents of objects and arrays that can be read inside of the browser console log.
*                   
*                   A tag can be set by passing a string that has the prefix TAG- as one of the arguments. Everytime a string with the TAG- prefix is
*                   detected, the tag is updated. This allows you to pass a tag that is applied to all data until it reaches another tag, which can then
*                   be applied to all data after it.
*
*                   Example:
*                   consoleLog('TAG-FirstTag',$data,$data2,'TAG-SecTag,$data3); 
*                   Result:
*                       FirstTag '...data...'
*                       FirstTag '...data2...'
*                       SecTag   '...data3...' 
*/
function consoleLog(){
    if(func_num_args() == 0){
        return;
    }

    $tag = '';
    for ($i = 0; $i < func_num_args(); $i++) {
        $arg = func_get_arg($i);
        if(!empty($arg)){       
            if(is_string($arg)&& strtolower(substr($arg,0,4)) === 'tag-'){
                $tag = substr($arg,4);
            }else{      
                $arg = json_encode($arg, JSON_HEX_TAG | JSON_HEX_AMP );
                echo "<script>console.log('".$tag." ".$arg."');</script>";
            }       
        }
    }
}

NOTE: func_num_args() and func_num_args() are php functions for reading a dynamic number of input args, and allow this function to have infinitely many console.log requests from one function call

I just want to add something relatively important about console.log

If you are debugging large variables (like large audio or video data buffers). When you print console.log(big_variable) the console will only display a small part of it. (it seems a bit obvious).

If however, the variable is in a loop and this variable is constantly changing, if you ever "copy it into your clipboard" , what the browser will do is to ask for the variable AGAIN (and that may have changed by the time you are copying).

I'll tell you my story. I am programming an app that deals with big chunks of audio data, with Float32arrays of size 8192. If the buffer had certain characteristics, I would print the variable using console.log() and then grab that variable to test and toy around and play with it (and even use it for mocks so I can do automated testing)

However, the results would never hold. The mic would capture the audio data, store it on a this.audioBuffer variable and the whole thing would work, but when I copied that exact variable from console.log so I could us it as a mock to run some automated tests, the behaviour would change dramatically.

It took me a while to figure this out, Apparently, whenever i "copied" or "set the variable as global" in the debugger, rather than copying the variables displayed in console.log, the jsvm would ask for the this.audioBuffer again. and since the variable was being used inside of a loop, the microphone would still record and I would get a completely different sound array than what I was listening to and thought the audio buffer was in the first place.

If you are dealing with large complex data structures like audio or video files, image files... and these are subject to change when you are reading the values in the chrome /firefox / edge console, make sure you don't console.log(variable), but rather console.log(JSON.stringify(variable)). it will save you a ton of time