JavaScript Does given String exists as variable and function
I have a variable with has a member variable which is a function
let test = {
setup: function() { ...}
}
From some other source, I get the String "test.setup"
How can i check if
a.) variable test exists
b.) variable test has a child called setup
c.) the child setup is a function ?
d.) call the function
I already tested
let variableName = "test.setup";
window[variableName]
// undefined
{}.toString.call(variableName ) === '[object Function]'
// VM2052:1 Uncaught SyntaxError: Unexpected token .
window.hasOwnProperty("test")
// false
It would be nice, if you could solve my problem. It would be enough for me to see if there is a such a function and call it if its there. Otherwise Inform the user that there is no such a function.
Thank you very much in advance
javascript
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
add a comment |
I have a variable with has a member variable which is a function
let test = {
setup: function() { ...}
}
From some other source, I get the String "test.setup"
How can i check if
a.) variable test exists
b.) variable test has a child called setup
c.) the child setup is a function ?
d.) call the function
I already tested
let variableName = "test.setup";
window[variableName]
// undefined
{}.toString.call(variableName ) === '[object Function]'
// VM2052:1 Uncaught SyntaxError: Unexpected token .
window.hasOwnProperty("test")
// false
It would be nice, if you could solve my problem. It would be enough for me to see if there is a such a function and call it if its there. Otherwise Inform the user that there is no such a function.
Thank you very much in advance
javascript
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
2
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things likeeval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.
– Mark Meyer
Jan 2 at 18:02
1
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
1
letandconsthave block scope, but if you declare the variable withvar, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it withvaroutside any functions, you can usewindow["variableNameHere"]to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.
– IceMetalPunk
Jan 2 at 18:20
add a comment |
I have a variable with has a member variable which is a function
let test = {
setup: function() { ...}
}
From some other source, I get the String "test.setup"
How can i check if
a.) variable test exists
b.) variable test has a child called setup
c.) the child setup is a function ?
d.) call the function
I already tested
let variableName = "test.setup";
window[variableName]
// undefined
{}.toString.call(variableName ) === '[object Function]'
// VM2052:1 Uncaught SyntaxError: Unexpected token .
window.hasOwnProperty("test")
// false
It would be nice, if you could solve my problem. It would be enough for me to see if there is a such a function and call it if its there. Otherwise Inform the user that there is no such a function.
Thank you very much in advance
javascript
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
I have a variable with has a member variable which is a function
let test = {
setup: function() { ...}
}
From some other source, I get the String "test.setup"
How can i check if
a.) variable test exists
b.) variable test has a child called setup
c.) the child setup is a function ?
d.) call the function
I already tested
let variableName = "test.setup";
window[variableName]
// undefined
{}.toString.call(variableName ) === '[object Function]'
// VM2052:1 Uncaught SyntaxError: Unexpected token .
window.hasOwnProperty("test")
// false
It would be nice, if you could solve my problem. It would be enough for me to see if there is a such a function and call it if its there. Otherwise Inform the user that there is no such a function.
Thank you very much in advance
javascript
javascript
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
asked Jan 2 at 17:58
MasterOfDesasterMasterOfDesaster
1136
1136
2
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things likeeval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.
– Mark Meyer
Jan 2 at 18:02
1
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
1
letandconsthave block scope, but if you declare the variable withvar, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it withvaroutside any functions, you can usewindow["variableNameHere"]to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.
– IceMetalPunk
Jan 2 at 18:20
add a comment |
2
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things likeeval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.
– Mark Meyer
Jan 2 at 18:02
1
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
1
letandconsthave block scope, but if you declare the variable withvar, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it withvaroutside any functions, you can usewindow["variableNameHere"]to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.
– IceMetalPunk
Jan 2 at 18:20
2
2
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things like
eval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.– Mark Meyer
Jan 2 at 18:02
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things like
eval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.– Mark Meyer
Jan 2 at 18:02
1
1
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
1
1
let and const have block scope, but if you declare the variable with var, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it with var outside any functions, you can use window["variableNameHere"] to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.– IceMetalPunk
Jan 2 at 18:20
let and const have block scope, but if you declare the variable with var, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it with var outside any functions, you can use window["variableNameHere"] to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.– IceMetalPunk
Jan 2 at 18:20
add a comment |
1 Answer
1
active
oldest
votes
The easiest and less secure way is to use eval(). Never use eval() with user generated data as it's an attack vector.
let test = { setup: function() { return "HelloWorld"; }
let x = eval("typeof test.setup");
console.log(typeof x); // prints function
console.log(x()); // prints "HelloWorld";
You will get an error if ".setup" is evaluated on an undefined variable. So you can use try/catch to handle this.
function exists(value) {
try {
return eval(value);
} catch(e) {
return undefined;
}
}
console.log(exists("typeof test.setup")); // prints a type if it exists, or undefined
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
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oldest
votes
active
oldest
votes
The easiest and less secure way is to use eval(). Never use eval() with user generated data as it's an attack vector.
let test = { setup: function() { return "HelloWorld"; }
let x = eval("typeof test.setup");
console.log(typeof x); // prints function
console.log(x()); // prints "HelloWorld";
You will get an error if ".setup" is evaluated on an undefined variable. So you can use try/catch to handle this.
function exists(value) {
try {
return eval(value);
} catch(e) {
return undefined;
}
}
console.log(exists("typeof test.setup")); // prints a type if it exists, or undefined
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
add a comment |
The easiest and less secure way is to use eval(). Never use eval() with user generated data as it's an attack vector.
let test = { setup: function() { return "HelloWorld"; }
let x = eval("typeof test.setup");
console.log(typeof x); // prints function
console.log(x()); // prints "HelloWorld";
You will get an error if ".setup" is evaluated on an undefined variable. So you can use try/catch to handle this.
function exists(value) {
try {
return eval(value);
} catch(e) {
return undefined;
}
}
console.log(exists("typeof test.setup")); // prints a type if it exists, or undefined
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
add a comment |
The easiest and less secure way is to use eval(). Never use eval() with user generated data as it's an attack vector.
let test = { setup: function() { return "HelloWorld"; }
let x = eval("typeof test.setup");
console.log(typeof x); // prints function
console.log(x()); // prints "HelloWorld";
You will get an error if ".setup" is evaluated on an undefined variable. So you can use try/catch to handle this.
function exists(value) {
try {
return eval(value);
} catch(e) {
return undefined;
}
}
console.log(exists("typeof test.setup")); // prints a type if it exists, or undefined
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
The easiest and less secure way is to use eval(). Never use eval() with user generated data as it's an attack vector.
let test = { setup: function() { return "HelloWorld"; }
let x = eval("typeof test.setup");
console.log(typeof x); // prints function
console.log(x()); // prints "HelloWorld";
You will get an error if ".setup" is evaluated on an undefined variable. So you can use try/catch to handle this.
function exists(value) {
try {
return eval(value);
} catch(e) {
return undefined;
}
}
console.log(exists("typeof test.setup")); // prints a type if it exists, or undefined
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
answered Jan 2 at 18:05
cgTagcgTag
24.3k864113
24.3k864113
add a comment |
add a comment |
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2
Needing to dynamically know the names of variables is often an xy problem and has a pretty strong code smell that leads to needing things like
eval(). If you need to dynamically access something with a string key, that something should be part of a larger data structure, then the problem goes away.– Mark Meyer
Jan 2 at 18:02
1
@MarkMeyer I agree. It's a symptom of a problem.
– cgTag
Jan 2 at 18:08
@MarkMeyer sometimes as developer you do not have the possibilities to change the bigger data structure and have to work with, what was given to you =(
– MasterOfDesaster
Jan 2 at 18:12
1
letandconsthave block scope, but if you declare the variable withvar, it'll have either global or local function scope (depending if it's declared inside a function or not). So if you declare it withvaroutside any functions, you can usewindow["variableNameHere"]to check if it exists. However, I do agree with the above: you should be defining it as an enclosed object and checking if the "variable name" exists as a key. If you can't access the original variable, at least you can copy it to one you can change.– IceMetalPunk
Jan 2 at 18:20