问题
I\'m using Firebug and have some statements like:
console.log(\"...\");
in my page. In IE8 (probably earlier versions too) I get script errors saying \'console\' is undefined. I tried putting this at the top of my page:
<script type=\"text/javascript\">
if (!console) console = {log: function() {}};
</script>
still I get the errors. Any way to get rid of the errors?
回答1:
Try
if (!window.console) console = ...
An undefined variable cannot be referred directly. However, all global variables are attributes of the same name of the global context (window in case of browsers), and accessing an undefined attribute is fine.
Or use if (typeof console === 'undefined') console = ... if you want to avoid the magic variable window, see @Tim Down's answer.
回答2:
Paste the following at the top of your JavaScript (before using the console):
/**
* Protect window.console method calls, e.g. console is not defined on IE
* unless dev tools are open, and IE doesn't define console.debug
*
* Chrome 41.0.2272.118: debug,error,info,log,warn,dir,dirxml,table,trace,assert,count,markTimeline,profile,profileEnd,time,timeEnd,timeStamp,timeline,timelineEnd,group,groupCollapsed,groupEnd,clear
* Firefox 37.0.1: log,info,warn,error,exception,debug,table,trace,dir,group,groupCollapsed,groupEnd,time,timeEnd,profile,profileEnd,assert,count
* Internet Explorer 11: select,log,info,warn,error,debug,assert,time,timeEnd,timeStamp,group,groupCollapsed,groupEnd,trace,clear,dir,dirxml,count,countReset,cd
* Safari 6.2.4: debug,error,log,info,warn,clear,dir,dirxml,table,trace,assert,count,profile,profileEnd,time,timeEnd,timeStamp,group,groupCollapsed,groupEnd
* Opera 28.0.1750.48: debug,error,info,log,warn,dir,dirxml,table,trace,assert,count,markTimeline,profile,profileEnd,time,timeEnd,timeStamp,timeline,timelineEnd,group,groupCollapsed,groupEnd,clear
*/
(function() {
// Union of Chrome, Firefox, IE, Opera, and Safari console methods
var methods = ["assert", "cd", "clear", "count", "countReset",
"debug", "dir", "dirxml", "error", "exception", "group", "groupCollapsed",
"groupEnd", "info", "log", "markTimeline", "profile", "profileEnd",
"select", "table", "time", "timeEnd", "timeStamp", "timeline",
"timelineEnd", "trace", "warn"];
var length = methods.length;
var console = (window.console = window.console || {});
var method;
var noop = function() {};
while (length--) {
method = methods[length];
// define undefined methods as noops to prevent errors
if (!console[method])
console[method] = noop;
}
})();
The function closure wrapper is to scope the variables as to not define any variables. This guards against both undefined console and undefined console.debug (and other missing methods).
EDIT: I noticed that HTML5 Boilerplate uses similar code in its js/plugins.js file, if you're looking for a solution that will (probably) be kept up-to-date.
回答3:
Another alternative is the typeof operator:
if (typeof console == "undefined") {
this.console = {log: function() {}};
}
Yet another alternative is to use a logging library, such as my own log4javascript.
回答4:
For a more robust solution, use this piece of code (taken from twitter's source code):
// Avoid `console` errors in browsers that lack a console.
(function() {
var method;
var noop = function () {};
var methods = [
'assert', 'clear', 'count', 'debug', 'dir', 'dirxml', 'error',
'exception', 'group', 'groupCollapsed', 'groupEnd', 'info', 'log',
'markTimeline', 'profile', 'profileEnd', 'table', 'time', 'timeEnd',
'timeStamp', 'trace', 'warn'
];
var length = methods.length;
var console = (window.console = window.console || {});
while (length--) {
method = methods[length];
// Only stub undefined methods.
if (!console[method]) {
console[method] = noop;
}
}
}());
回答5:
In my scripts, I either use the shorthand:
window.console && console.log(...) // only log if the function exists
or, if it's not possible or feasible to edit every console.log line, I create a fake console:
// check to see if console exists. If not, create an empty object for it,
// then create and empty logging function which does nothing.
//
// REMEMBER: put this before any other console.log calls
!window.console && (window.console = {} && window.console.log = function () {});
回答6:
You can use console.log() if you have Developer Tools in IE8 opened and also you can use the Console textbox on script tab.
回答7:
if (typeof console == "undefined") {
this.console = {
log: function() {},
info: function() {},
error: function() {},
warn: function() {}
};
}
回答8:
Based on two previous answers by
- Vinícius Moraes
- Peter Tseng
and the documentations for
- Internet Explorer (IE 10)
- Safari (2012. 07. 23.)
- Firefox (2013. 05. 20.)
- Chrome (2013. 01. 25.) and Chrome (2012. 10. 04.)
- and some of my knowledge
Here's a best effort implementation for the issue, meaning if there's a console.log which actually exists, it fills in the gaps for non-existing methods via console.log.
For example for IE6/7 you can replace logging with alert (stupid but works) and then include the below monster (I called it console.js): [Feel free to remove comments as you see fit, I left them in for reference, a minimizer can tackle them]:
<!--[if lte IE 7]>
<SCRIPT LANGUAGE="javascript">
(window.console = window.console || {}).log = function() { return window.alert.apply(window, arguments); };
</SCRIPT>
<![endif]-->
<script type="text/javascript" src="console.js"></script>
and console.js:
/**
* Protect window.console method calls, e.g. console is not defined on IE
* unless dev tools are open, and IE doesn't define console.debug
*/
(function() {
var console = (window.console = window.console || {});
var noop = function () {};
var log = console.log || noop;
var start = function(name) { return function(param) { log("Start " + name + ": " + param); } };
var end = function(name) { return function(param) { log("End " + name + ": " + param); } };
var methods = {
// Internet Explorer (IE 10): http://msdn.microsoft.com/en-us/library/ie/hh772169(v=vs.85).aspx#methods
// assert(test, message, optionalParams), clear(), count(countTitle), debug(message, optionalParams), dir(value, optionalParams), dirxml(value), error(message, optionalParams), group(groupTitle), groupCollapsed(groupTitle), groupEnd([groupTitle]), info(message, optionalParams), log(message, optionalParams), msIsIndependentlyComposed(oElementNode), profile(reportName), profileEnd(), time(timerName), timeEnd(timerName), trace(), warn(message, optionalParams)
// "assert", "clear", "count", "debug", "dir", "dirxml", "error", "group", "groupCollapsed", "groupEnd", "info", "log", "msIsIndependentlyComposed", "profile", "profileEnd", "time", "timeEnd", "trace", "warn"
// Safari (2012. 07. 23.): https://developer.apple.com/library/safari/#documentation/AppleApplications/Conceptual/Safari_Developer_Guide/DebuggingYourWebsite/DebuggingYourWebsite.html#//apple_ref/doc/uid/TP40007874-CH8-SW20
// assert(expression, message-object), count([title]), debug([message-object]), dir(object), dirxml(node), error(message-object), group(message-object), groupEnd(), info(message-object), log(message-object), profile([title]), profileEnd([title]), time(name), markTimeline("string"), trace(), warn(message-object)
// "assert", "count", "debug", "dir", "dirxml", "error", "group", "groupEnd", "info", "log", "profile", "profileEnd", "time", "markTimeline", "trace", "warn"
// Firefox (2013. 05. 20.): https://developer.mozilla.org/en-US/docs/Web/API/console
// debug(obj1 [, obj2, ..., objN]), debug(msg [, subst1, ..., substN]), dir(object), error(obj1 [, obj2, ..., objN]), error(msg [, subst1, ..., substN]), group(), groupCollapsed(), groupEnd(), info(obj1 [, obj2, ..., objN]), info(msg [, subst1, ..., substN]), log(obj1 [, obj2, ..., objN]), log(msg [, subst1, ..., substN]), time(timerName), timeEnd(timerName), trace(), warn(obj1 [, obj2, ..., objN]), warn(msg [, subst1, ..., substN])
// "debug", "dir", "error", "group", "groupCollapsed", "groupEnd", "info", "log", "time", "timeEnd", "trace", "warn"
// Chrome (2013. 01. 25.): https://developers.google.com/chrome-developer-tools/docs/console-api
// assert(expression, object), clear(), count(label), debug(object [, object, ...]), dir(object), dirxml(object), error(object [, object, ...]), group(object[, object, ...]), groupCollapsed(object[, object, ...]), groupEnd(), info(object [, object, ...]), log(object [, object, ...]), profile([label]), profileEnd(), time(label), timeEnd(label), timeStamp([label]), trace(), warn(object [, object, ...])
// "assert", "clear", "count", "debug", "dir", "dirxml", "error", "group", "groupCollapsed", "groupEnd", "info", "log", "profile", "profileEnd", "time", "timeEnd", "timeStamp", "trace", "warn"
// Chrome (2012. 10. 04.): https://developers.google.com/web-toolkit/speedtracer/logging-api
// markTimeline(String)
// "markTimeline"
assert: noop, clear: noop, trace: noop, count: noop, timeStamp: noop, msIsIndependentlyComposed: noop,
debug: log, info: log, log: log, warn: log, error: log,
dir: log, dirxml: log, markTimeline: log,
group: start('group'), groupCollapsed: start('groupCollapsed'), groupEnd: end('group'),
profile: start('profile'), profileEnd: end('profile'),
time: start('time'), timeEnd: end('time')
};
for (var method in methods) {
if ( methods.hasOwnProperty(method) && !(method in console) ) { // define undefined methods as best-effort methods
console[method] = methods[method];
}
}
})();
回答9:
In IE9, if console is not opened, this code:
alert(typeof console);
will show "object", but this code
alert(typeof console.log);
will throw TypeError exception, but not return undefined value;
So, guaranteed version of code will look similar to this:
try {
if (window.console && window.console.log) {
my_console_log = window.console.log;
}
} catch (e) {
my_console_log = function() {};
}
回答10:
I am only using console.log in my code. So I include a very short 2 liner
var console = console || {};
console.log = console.log || function(){};
回答11:
Noticed that OP is using Firebug with IE, so assume it's Firebug Lite. This is a funky situation as console gets defined in IE when the debugger window is opened, but what happens when Firebug is already running? Not sure, but perhaps the "firebugx.js" method might be a good way to test in this situation:
source:
https://code.google.com/p/fbug/source/browse/branches/firebug1.2/lite/firebugx.js?r=187
if (!window.console || !console.firebug) {
var names = [
"log", "debug", "info", "warn", "error", "assert",
"dir","dirxml","group","groupEnd","time","timeEnd",
"count","trace","profile","profileEnd"
];
window.console = {};
for (var i = 0; i < names.length; ++i)
window.console[names[i]] = function() {}
}
(updated links 12/2014)
回答12:
I'm using fauxconsole; I modified the css a bit so that it looks nicer but works very well.
回答13:
For debugging in IE, check out this log4javascript
回答14:
For IE8 or console support limited to console.log (no debug, trace, ...) you can do the following:
If console OR console.log undefined: Create dummy functions for console functions (trace, debug, log, ...)
window.console = { debug : function() {}, ...};Else if console.log is defined (IE8) AND console.debug (any other) is not defined: redirect all logging functions to console.log, this allows to keep those logs !
window.console = { debug : window.console.log, ...};
Not sure about the assert support in various IE versions, but any suggestions are welcome. Also posted this answer here: How can I use console logging in Internet Explorer?
回答15:
console = console || {
debug: function(){},
log: function(){}
...
}
回答16:
Stub of console in TypeScript:
if (!window.console) {
console = {
assert: () => { },
clear: () => { },
count: () => { },
debug: () => { },
dir: () => { },
dirxml: () => { },
error: () => { },
group: () => { },
groupCollapsed: () => { },
groupEnd: () => { },
info: () => { },
log: () => { },
msIsIndependentlyComposed: (e: Element) => false,
profile: () => { },
profileEnd: () => { },
select: () => { },
time: () => { },
timeEnd: () => { },
trace: () => { },
warn: () => { },
}
};
回答17:
You can use the below to give an extra degree of insurance that you've got all bases covered. Using typeof first will avoid any undefined errors. Using === will also ensure that the name of the type is actually the string "undefined". Finally, you'll want to add a parameter to the function signature (I chose logMsg arbitrarily) to ensure consistency, since you do pass whatever you want printed to the console to the log function. This also keep you intellisense accurate and avoids any warnings/errors in your JS aware IDE.
if(!window.console || typeof console === "undefined") {
var console = { log: function (logMsg) { } };
}
回答18:
Sometimes console will work in IE8/9 but fail at other times. This erratic behaviour depends on whether you have developer tools open and is described in stackoverflow question Does IE9 support console.log, and is it a real function?
回答19:
Encountered similar problem running console.log in child windows in IE9, created by window.open function.
It seems that in this case console is defined only in parent window and is undefined in child windows until you refresh them. Same applies to children of child windows.
I deal with this issue by wrapping log in next function (below is fragment of module)
getConsole: function()
{
if (typeof console !== 'undefined') return console;
var searchDepthMax = 5,
searchDepth = 0,
context = window.opener;
while (!!context && searchDepth < searchDepthMax)
{
if (typeof context.console !== 'undefined') return context.console;
context = context.opener;
searchDepth++;
}
return null;
},
log: function(message){
var _console = this.getConsole();
if (!!_console) _console.log(message);
}
回答20:
After having oh so many problems with this thing (it's hard to debug the error since if you open the developer console the error no longer happens!) I decided to make an overkill code to never have to bother with this ever again:
if (typeof window.console === "undefined")
window.console = {};
if (typeof window.console.debug === "undefined")
window.console.debug= function() {};
if (typeof window.console.log === "undefined")
window.console.log= function() {};
if (typeof window.console.error === "undefined")
window.console.error= function() {alert("error");};
if (typeof window.console.time === "undefined")
window.console.time= function() {};
if (typeof window.console.trace === "undefined")
window.console.trace= function() {};
if (typeof window.console.info === "undefined")
window.console.info= function() {};
if (typeof window.console.timeEnd === "undefined")
window.console.timeEnd= function() {};
if (typeof window.console.group === "undefined")
window.console.group= function() {};
if (typeof window.console.groupEnd === "undefined")
window.console.groupEnd= function() {};
if (typeof window.console.groupCollapsed === "undefined")
window.console.groupCollapsed= function() {};
if (typeof window.console.dir === "undefined")
window.console.dir= function() {};
if (typeof window.console.warn === "undefined")
window.console.warn= function() {};
Personaly I only ever use console.log and console.error, but this code handles all the other functions as shown in the Mozzila Developer Network: https://developer.mozilla.org/en-US/docs/Web/API/console. Just put that code on the top of your page and you are done forever with this.
回答21:
You can use console.log(...) directly in Firefox but not in IEs. In IEs you have to use window.console.
来源：https://stackoverflow.com/questions/3326650/console-is-undefined-error-for-internet-explorer