Determine whether a function or variable exists in JavaScript.

Determine whether a function or variable exists in JavaScript.

1. Whether a specified function exists
Copy codeThe Code is as follows:
Function isExitsFunction (funcName ){
Try {
If (typeof (eval (funcName) = "function "){
Return true;
}
} Catch (e ){}
Return false;
}

2. Similar to common PHP functions to determine whether a function exists, a function is created if it does not exist.
Copy codeThe Code is as follows:
If (typeof String. prototype. endsWith! = 'Function '){
String. prototype. endsWith = function (suffix ){
Return this. indexOf (suffix, this. length-suffix. length )! =-1;
};
}

3. Determine whether a js function exists. If yes, execute

Assume that funcName is the function name. Use the following method to achieve the goal:

You must add a try catch block. Otherwise, it does not work.
Copy codeThe Code is as follows:
Try
{
If (typeof (eval (funcName) = "function ")
{
FuncName ();
}
} Catch (e)
{
// Alert ("not function ");
}

Iv. Whether a specified variable exists
Copy codeThe Code is as follows:
Function isExitsVariable (variableName ){
Try {
If (typeof (variableName) = "undefined "){
// Alert ("value is undefined ");
Return false;
} Else {
// Alert ("value is true ");
Return true;
}
} Catch (e ){}
Return false;
}