Assign console.log value to a variable - javascript

How can I assign a JavaScript object to a variable which was printed using console.log?
I am in Chrome console. With Ruby I would use test = _ to access the most recent item printed.

If you want to do this to an object that has been already logged (one time thing), chrome console offers a good solution.
Hover over the printed object in the console, right click, then click on "Store as Global Variable". Chrome will assign it to a temporary var name for you which you can use in the console.

You could override standard console.log() function with your own, adding the behaviour you need:
console.oldLog = console.log;
console.log = function(value)
{
console.oldLog(value);
window.$log = value;
};
// Usage
console.log('hello');
$log // Has 'hello' in it
This way, you don't have to change your existing logging code. You could also extend it adding an array and storing the whole history of printed objects/values.

In Chrome developer tools, you may access last item by $_:
> 1+1;
2
> $_
2

Derivative of mirrormx's answer, but more convenient. I don't need to write a function and can just put it in anywhere on the spur of the moment.
console.log(window.$log = data);

Here is chrome reference for comand line api.
There is $_ variable but it "Returns the value of the most recently evaluated expression" not printed, you can make your own log function like this:
function log(data){
console.log(data);
return data;
}
// after that you can access last printed value by $_
Please, note that my function is for example, console.log possibilities is much more advanced

Related

Variable undefined result [duplicate]

Every time console.log is executed, a line saying undefined is appended to the output log.
It happens in both Firefox and Chrome on Windows and Linux.
If you're running console.log() from a JS file, this undefined line should not be appended.
If you're running console.log() from the console itself, it makes sense. This is why: In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.
I tested both cases on my Chrome (Mac ver 23.0.1271.101) and indeed I see the undefined line when I run it inside the console. This undefined also appears when I write this line in the console: var bla = "sdfdfs"
Although talkol´s answer is ok, I try to put it more straight:
JavaScript is designed as a dynamic language which means that the type (string, void, boolean …) of a function return value is not pre-defined. If a function does not use a return statement or an empty return statement with no value, JavaScript automatically returns undefined. That means that in JavaScript every function returns something, at least undefined.
So the function console.log() in Chrome console either uses no or an empty return statement, so that the return value of this function is undefined. This function return value gets also displayed in the Chrome console.
[If somebody know where to find the definition of the console.log() function in Google Chrome source code, please comment with the link, then we can even go further and look at the real code, would be nice.]
Sources:
https://stackoverflow.com/a/20915524/1744768
https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript
Follow the picture to solve this problem:
Ctrl + Shift + J
Console environment in your browser is designed to take the very last statement expression in a program and evaluate it for a value and then show you that value.
The result of an assignment expression is the value that was assigned.
So the JavaScript engine just does an assignment but the console does one extra step which is to set whatever my last statement is, give you that value back. That’s why it prints 2:
In statements that have no return value you get something like undefined.
undefined is the return value of the console.log() in Chrome developer tools. You will get undefined if you do the following in Chrome developer tools, and you will see that you get undefined even though x has the value 3.
> let x = 3
> undefined
What you can do is simply create your own console.log like function with a return to change this behavior when doing a lot of coding in the developer console. Here is an example of what that looks like in the developer console:
console.log('I hate seeing the next line stating the obvious.')
I hate seeing the next line stating the obvious.
undefined
log = function(l){return l}
function log()
if(1 === 2){console.log('1 is not equal to 2.')}else{log('No Shit Sherlock.')}
"No Shit Sherlock."
That undefined you see in console is the return value of the function:
check out these two variants:
This one returns nothing
This one returns something:
Remember one thing. Any function that has some definition will always return something, If you skip the return keyword, it will eventually return undefined when you call it.
If you're using console.log to emit multiple values in a single line, here's a hacky alternative:
var1 + ' ' + var2 + ' ' + var...
(Better ideas welcome, this might blow up in certain circumstances)

ES6 : Output contains undefined along with results and I cannot understand why? [duplicate]

Every time console.log is executed, a line saying undefined is appended to the output log.
It happens in both Firefox and Chrome on Windows and Linux.
If you're running console.log() from a JS file, this undefined line should not be appended.
If you're running console.log() from the console itself, it makes sense. This is why: In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.
I tested both cases on my Chrome (Mac ver 23.0.1271.101) and indeed I see the undefined line when I run it inside the console. This undefined also appears when I write this line in the console: var bla = "sdfdfs"
Although talkol´s answer is ok, I try to put it more straight:
JavaScript is designed as a dynamic language which means that the type (string, void, boolean …) of a function return value is not pre-defined. If a function does not use a return statement or an empty return statement with no value, JavaScript automatically returns undefined. That means that in JavaScript every function returns something, at least undefined.
So the function console.log() in Chrome console either uses no or an empty return statement, so that the return value of this function is undefined. This function return value gets also displayed in the Chrome console.
[If somebody know where to find the definition of the console.log() function in Google Chrome source code, please comment with the link, then we can even go further and look at the real code, would be nice.]
Sources:
https://stackoverflow.com/a/20915524/1744768
https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript
Follow the picture to solve this problem:
Ctrl + Shift + J
Console environment in your browser is designed to take the very last statement expression in a program and evaluate it for a value and then show you that value.
The result of an assignment expression is the value that was assigned.
So the JavaScript engine just does an assignment but the console does one extra step which is to set whatever my last statement is, give you that value back. That’s why it prints 2:
In statements that have no return value you get something like undefined.
undefined is the return value of the console.log() in Chrome developer tools. You will get undefined if you do the following in Chrome developer tools, and you will see that you get undefined even though x has the value 3.
> let x = 3
> undefined
What you can do is simply create your own console.log like function with a return to change this behavior when doing a lot of coding in the developer console. Here is an example of what that looks like in the developer console:
console.log('I hate seeing the next line stating the obvious.')
I hate seeing the next line stating the obvious.
undefined
log = function(l){return l}
function log()
if(1 === 2){console.log('1 is not equal to 2.')}else{log('No Shit Sherlock.')}
"No Shit Sherlock."
That undefined you see in console is the return value of the function:
check out these two variants:
This one returns nothing
This one returns something:
Remember one thing. Any function that has some definition will always return something, If you skip the return keyword, it will eventually return undefined when you call it.
If you're using console.log to emit multiple values in a single line, here's a hacky alternative:
var1 + ' ' + var2 + ' ' + var...
(Better ideas welcome, this might blow up in certain circumstances)

Why does only the last function display on the console? [duplicate]

Every time console.log is executed, a line saying undefined is appended to the output log.
It happens in both Firefox and Chrome on Windows and Linux.
If you're running console.log() from a JS file, this undefined line should not be appended.
If you're running console.log() from the console itself, it makes sense. This is why: In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.
I tested both cases on my Chrome (Mac ver 23.0.1271.101) and indeed I see the undefined line when I run it inside the console. This undefined also appears when I write this line in the console: var bla = "sdfdfs"
Although talkol´s answer is ok, I try to put it more straight:
JavaScript is designed as a dynamic language which means that the type (string, void, boolean …) of a function return value is not pre-defined. If a function does not use a return statement or an empty return statement with no value, JavaScript automatically returns undefined. That means that in JavaScript every function returns something, at least undefined.
So the function console.log() in Chrome console either uses no or an empty return statement, so that the return value of this function is undefined. This function return value gets also displayed in the Chrome console.
[If somebody know where to find the definition of the console.log() function in Google Chrome source code, please comment with the link, then we can even go further and look at the real code, would be nice.]
Sources:
https://stackoverflow.com/a/20915524/1744768
https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript
Follow the picture to solve this problem:
Ctrl + Shift + J
Console environment in your browser is designed to take the very last statement expression in a program and evaluate it for a value and then show you that value.
The result of an assignment expression is the value that was assigned.
So the JavaScript engine just does an assignment but the console does one extra step which is to set whatever my last statement is, give you that value back. That’s why it prints 2:
In statements that have no return value you get something like undefined.
undefined is the return value of the console.log() in Chrome developer tools. You will get undefined if you do the following in Chrome developer tools, and you will see that you get undefined even though x has the value 3.
> let x = 3
> undefined
What you can do is simply create your own console.log like function with a return to change this behavior when doing a lot of coding in the developer console. Here is an example of what that looks like in the developer console:
console.log('I hate seeing the next line stating the obvious.')
I hate seeing the next line stating the obvious.
undefined
log = function(l){return l}
function log()
if(1 === 2){console.log('1 is not equal to 2.')}else{log('No Shit Sherlock.')}
"No Shit Sherlock."
That undefined you see in console is the return value of the function:
check out these two variants:
This one returns nothing
This one returns something:
Remember one thing. Any function that has some definition will always return something, If you skip the return keyword, it will eventually return undefined when you call it.
If you're using console.log to emit multiple values in a single line, here's a hacky alternative:
var1 + ' ' + var2 + ' ' + var...
(Better ideas welcome, this might blow up in certain circumstances)

How to store HTML Elements as global variable in the console

When I use chrome developper tools, for any variable that I logged to the console using console.log, I can right-click and select Store as global variable, except if I log a HTML Element.
I found a workaround: if using console.log([el]) instead of console.log(el), it is possible to save the array to a global variable and then use temp1[0] to access the element.
This seems somehow cumbersome. Is there another way to store a console.logged element in a global variable in the console ?
You can use $$(selector)
ƒ $$(selector, [startNode]) { [Command Line API] }
then use the procedure described at the Question.
$_ returns the last logged item in the console.
Beware, though, that it might return undefined if you use console.log(), because if you do console.log('hi!');, then it will also return undefined. To workaround:
/*just type value instead of console.log*/
'hello!';
var text=$_;
/*If you cannot do this, just log it in this way:*/
x.valueOf();
var xContent=$_;

JavaScript - Different outputs on different compiler (undefined on Chrome) [duplicate]

Every time console.log is executed, a line saying undefined is appended to the output log.
It happens in both Firefox and Chrome on Windows and Linux.
If you're running console.log() from a JS file, this undefined line should not be appended.
If you're running console.log() from the console itself, it makes sense. This is why: In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.
I tested both cases on my Chrome (Mac ver 23.0.1271.101) and indeed I see the undefined line when I run it inside the console. This undefined also appears when I write this line in the console: var bla = "sdfdfs"
Although talkol´s answer is ok, I try to put it more straight:
JavaScript is designed as a dynamic language which means that the type (string, void, boolean …) of a function return value is not pre-defined. If a function does not use a return statement or an empty return statement with no value, JavaScript automatically returns undefined. That means that in JavaScript every function returns something, at least undefined.
So the function console.log() in Chrome console either uses no or an empty return statement, so that the return value of this function is undefined. This function return value gets also displayed in the Chrome console.
[If somebody know where to find the definition of the console.log() function in Google Chrome source code, please comment with the link, then we can even go further and look at the real code, would be nice.]
Sources:
https://stackoverflow.com/a/20915524/1744768
https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript
Follow the picture to solve this problem:
Ctrl + Shift + J
Console environment in your browser is designed to take the very last statement expression in a program and evaluate it for a value and then show you that value.
The result of an assignment expression is the value that was assigned.
So the JavaScript engine just does an assignment but the console does one extra step which is to set whatever my last statement is, give you that value back. That’s why it prints 2:
In statements that have no return value you get something like undefined.
undefined is the return value of the console.log() in Chrome developer tools. You will get undefined if you do the following in Chrome developer tools, and you will see that you get undefined even though x has the value 3.
> let x = 3
> undefined
What you can do is simply create your own console.log like function with a return to change this behavior when doing a lot of coding in the developer console. Here is an example of what that looks like in the developer console:
console.log('I hate seeing the next line stating the obvious.')
I hate seeing the next line stating the obvious.
undefined
log = function(l){return l}
function log()
if(1 === 2){console.log('1 is not equal to 2.')}else{log('No Shit Sherlock.')}
"No Shit Sherlock."
That undefined you see in console is the return value of the function:
check out these two variants:
This one returns nothing
This one returns something:
Remember one thing. Any function that has some definition will always return something, If you skip the return keyword, it will eventually return undefined when you call it.
If you're using console.log to emit multiple values in a single line, here's a hacky alternative:
var1 + ' ' + var2 + ' ' + var...
(Better ideas welcome, this might blow up in certain circumstances)

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