I see this in some JavaScript files:
console.log(algumaCoisa);
console.log("alguma coisa");
What is it good for and how does it work?
I'm trying to make a custom log() for a Userscript (see How can I log information without using alert in userscripts ) and I realized that I do not know what's behind console.log .
console is effectively an object with several associated methods.
The console object provides access to the browser debug console. The operation of this object varies from browser to browser but there are certain methods that are seen as a standard. One of these methods is log() .
The log() method exists essentially to allow data to be sent to the browser debug console. Any information can be sent, usually for debugging code.
Example of the Firefox console:
Clickctrl+shift+ktocallitinFirefox.
Asthisobjectvariesandthereisstillnostandardtogovernitsoperationandmethodology,therearesomeconsiderationstohave:
// Exemplo a enviar algo para a consola do navegador
var s = "bubu";
console.log(s);
In JavaScript, a runtime failure can result in a blocking of all other JavaScript. If for example we use console.log(X) when the console does not exist or the log() method does not exist, we will have an error in our code.
We can make use of a try...catch to try to send to the console and in case of failure to act otherwise:
function consola(s) {
try { console.log(s); } catch (e) { alert(s); }
}
And so if it goes well, the information will be in the console, if it goes bad it will be emitted a alert() with the information that would go to the console.
Of course we can do nothing or send an Ajax call to a server with the error if it is critical and has to be registered "give to anyone who hurts."
/* Enviar algo para a consola do navegador com fallback
* fazendo uso da função já declarada conforme visto em cima
*/
var s = "bubu";
consola(s);
As explained, there is not really a standard for the web console, so there are some references to the help pages for each one:
Note: Response to evolve within a few days as you finish compiling more relevant information on this subject.
This writes any message in the browser LOG, which can be viewed at any time.
These messages can be used for various purposes:
alert would be more recommended. Other existing LOG methods:
console.warn console.info console.warn console.error They all serve to write messages, the difference between methods is precisely in the meaning of the message. Here's how the messages get with each of these methods:
(example: chrome console window)
console.log is one of a number of other methods available for the browsers debug console .
List of other console methods . p>
console.log is used for the issuance of registration information in general. For example:
var algumObjeto = {
str: "Algum texto",
id: 5
};
console.log(algumObjeto);
Output:
({str:"Algum texto", id:5})
var algumObjeto = {
str: "Algum texto",
id: 5
};
console.log(algumObjeto);Observar a saída no console do navegador!You can also use string substitution and other arguments with this method. For example:
for (var i=0; i<5; i++) {
console.log("Olá, %s. Você me chamou pela %dª vez.", "João", i+1);
}
Output:
Olá, João. Você me chamou pela 1ª vez.
Olá, João. Você me chamou pela 2ª vez.
Olá, João. Você me chamou pela 3ª vez.
Olá, João. Você me chamou pela 4ª vez.
Olá, João. Você me chamou pela 5ª vez.
for (var i = 0; i < 5; i++) {
console.log("Olá, %s. Você me chamou pela %dª vez.", "João", i + 1);
}<p>Observar a saída no console do navegador!</p>Limitations and lack of support
This feature may not be available or active in the browser, so you should always test its existence before attempting to use it:
// verifica se o objeto window.console existe
if (window.console){
window.console.log("Log isto");
}
Important notes
In addition to the situations mentioned above, old versions of IE, or < IE9 , do not present this method as previously presented (with the same name / signature) or do not present, as quoted in those references:
Source: MDN Console
A way to debug your code. This command will show in the console of your browser what is written in the log function.