Чтобы ответить на вопрос из контекста заголовка этого вопроса, вот функция, которая делает что-то похожее на PHP var_dump. Он выводит только одну переменную за вызов, но указывает тип данных, а также значение и выполняет итерацию по массивам и объектам [даже если они являются массивами объектов и наоборот]. Я уверен, что это можно улучшить. Я скорее парень из PHP.
/**
* Does a PHP var_dump'ish behavior. It only dumps one variable per call. The
* first parameter is the variable, and the second parameter is an optional
* name. This can be the variable name [makes it easier to distinguish between
* numerious calls to this function], but any string value can be passed.
*
* @param mixed var_value - the variable to be dumped
* @param string var_name - ideally the name of the variable, which will be used
* to label the dump. If this argumment is omitted, then the dump will
* display without a label.
* @param boolean - annonymous third parameter.
* On TRUE publishes the result to the DOM document body.
* On FALSE a string is returned.
* Default is TRUE.
* @returns string|inserts Dom Object in the BODY element.
*/
function my_dump (var_value, var_name)
{
// Check for a third argument and if one exists, capture it's value, else
// default to TRUE. When the third argument is true, this function
// publishes the result to the document body, else, it outputs a string.
// The third argument is intend for use by recursive calls within this
// function, but there is no reason why it couldn't be used in other ways.
var is_publish_to_body = typeof arguments[2] === 'undefined' ? true:arguments[2];
// Check for a fourth argument and if one exists, add three to it and
// use it to indent the out block by that many characters. This argument is
// not intended to be used by any other than the recursive call.
var indent_by = typeof arguments[3] === 'undefined' ? 0:arguments[3]+3;
var do_boolean = function (v)
{
return 'Boolean(1) '+(v?'TRUE':'FALSE');
};
var do_number = function(v)
{
var num_digits = (''+v).length;
return 'Number('+num_digits+') '+v;
};
var do_string = function(v)
{
var num_chars = v.length;
return 'String('+num_chars+') "'+v+'"';
};
var do_object = function(v)
{
if (v === null)
{
return "NULL(0)";
}
var out = '';
var num_elem = 0;
var indent = '';
if (v instanceof Array)
{
num_elem = v.length;
for (var d=0; d<indent_by; ++d)
{
indent += ' ';
}
out = "Array("+num_elem+") \n"+(indent.length === 0?'':'|'+indent+'')+"(";
for (var i=0; i<num_elem; ++i)
{
out += "\n"+(indent.length === 0?'':'|'+indent)+"| ["+i+"] = "+my_dump(v[i],'',false,indent_by);
}
out += "\n"+(indent.length === 0?'':'|'+indent+'')+")";
return out;
}
else if (v instanceof Object)
{
for (var d=0; d<indent_by; ++d)
{
indent += ' ';
}
out = "Object \n"+(indent.length === 0?'':'|'+indent+'')+"(";
for (var p in v)
{
out += "\n"+(indent.length === 0?'':'|'+indent)+"| ["+p+"] = "+my_dump(v[p],'',false,indent_by);
}
out += "\n"+(indent.length === 0?'':'|'+indent+'')+")";
return out;
}
else
{
return 'Unknown Object Type!';
}
};
// Makes it easier, later on, to switch behaviors based on existance or
// absence of a var_name parameter. By converting 'undefined' to 'empty
// string', the length greater than zero test can be applied in all cases.
var_name = typeof var_name === 'undefined' ? '':var_name;
var out = '';
var v_name = '';
switch (typeof var_value)
{
case "boolean":
v_name = var_name.length > 0 ? var_name + ' = ':''; // Turns labeling on if var_name present, else no label
out += v_name + do_boolean(var_value);
break;
case "number":
v_name = var_name.length > 0 ? var_name + ' = ':'';
out += v_name + do_number(var_value);
break;
case "string":
v_name = var_name.length > 0 ? var_name + ' = ':'';
out += v_name + do_string(var_value);
break;
case "object":
v_name = var_name.length > 0 ? var_name + ' => ':'';
out += v_name + do_object(var_value);
break;
case "function":
v_name = var_name.length > 0 ? var_name + ' = ':'';
out += v_name + "Function";
break;
case "undefined":
v_name = var_name.length > 0 ? var_name + ' = ':'';
out += v_name + "Undefined";
break;
default:
out += v_name + ' is unknown type!';
}
// Using indent_by to filter out recursive calls, so this only happens on the
// primary call [i.e. at the end of the algorithm]
if (is_publish_to_body && indent_by === 0)
{
var div_dump = document.getElementById('div_dump');
if (!div_dump)
{
div_dump = document.createElement('div');
div_dump.id = 'div_dump';
var style_dump = document.getElementsByTagName("style")[0];
if (!style_dump)
{
var head = document.getElementsByTagName("head")[0];
style_dump = document.createElement("style");
head.appendChild(style_dump);
}
// Thank you Tim Down [http://stackoverflow.com/users/96100/tim-down]
// for the following addRule function
var addRule;
if (typeof document.styleSheets != "undefined" && document.styleSheets) {
addRule = function(selector, rule) {
var styleSheets = document.styleSheets, styleSheet;
if (styleSheets && styleSheets.length) {
styleSheet = styleSheets[styleSheets.length - 1];
if (styleSheet.addRule) {
styleSheet.addRule(selector, rule)
} else if (typeof styleSheet.cssText == "string") {
styleSheet.cssText = selector + " {" + rule + "}";
} else if (styleSheet.insertRule && styleSheet.cssRules) {
styleSheet.insertRule(selector + " {" + rule + "}", styleSheet.cssRules.length);
}
}
};
} else {
addRule = function(selector, rule, el, doc) {
el.appendChild(doc.createTextNode(selector + " {" + rule + "}"));
};
}
// Ensure the dump text will be visible under all conditions [i.e. always
// black text against a white background].
addRule('#div_dump', 'background-color:white', style_dump, document);
addRule('#div_dump', 'color:black', style_dump, document);
addRule('#div_dump', 'padding:15px', style_dump, document);
style_dump = null;
}
var pre_dump = document.getElementById('pre_dump');
if (!pre_dump)
{
pre_dump = document.createElement('pre');
pre_dump.id = 'pre_dump';
pre_dump.innerHTML = out+"\n";
div_dump.appendChild(pre_dump);
document.body.appendChild(div_dump);
}
else
{
pre_dump.innerHTML += out+"\n";
}
}
else
{
return out;
}
}