JS to determine if a specified variable or function exists

Source: Internet
Author: User
Whether the specified variable exists
function Isexitsvariable (variableName) {
try {
if (typeof (Eval (variableName)) = = "undefined") {
Console.log ("declared variable, but not initialized");
return false;
} else {
Console.log ("The variable has been declared and has been initialized");
return true;
} catch (e) {
Console.log ("Non-declared variable");
return false;

Whether the specified function exists
function Isexitsfunction (funcName) {    try {        if (typeof (eval (funcName) = = "function") {            return true;        }    } catch (e) {}    return false;}

Call Method:

Alert (isexitsvariable (' xx '));

var xx;

Alert (isexitsvariable (' xx '));

var xx = 123;

Alert (isexitsvariable (' xx '));

JS to determine if a specified variable or function exists

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