Typically, when faced with a question like this, it often points to an X/Y dilemma: You are trying to achieve X, you believe Y is the solution, so you attempt Y and then seek help on how to make Y work. In such cases, it might be more beneficial to inquire about how to accomplish X directly.
Addressing the specific query at hand: One potential approach is to utilize replacer and reviver functions to transform the function into a string (during stringify) and back into a function (during parse) in order to store a string representation of the function. However, there are several concerns associated with this method, particularly the scope in which the function is defined which can significantly impact its behavior. Furthermore, converting a string from local storage into executable code involves trusting that the content in local storage has not been tampered with maliciously, posing a security risk to consider.
Although provided below is an example illustrating this technique, I do not recommend employing it unless all other alternatives have been exhausted, primarily due to its reliance on eval, which can introduce vulnerabilities:
// Object containing a function
var obj = {
a: 5,
b: function (param) {
return param;
}
};
// Converting to JSON utilizing a replacer function
var json = JSON.stringify(obj, function(key, value) {
if (typeof value === "function") {
return "/Function(" + value.toString() + ")/";
}
return value;
});
// Converting back to an object using a reviver function
var obj2 = JSON.parse(json, function(key, value) {
if (typeof value === "string" &&
value.startsWith("/Function(") &&
value.endsWith(")/")) {
value = value.substring(10, value.length - 2);
return (0, eval)("(" + value + ")");
}
return value;
});
document.body.innerHTML = obj2.b(42);
The expression (0, eval)("(" + value + ")");
ensures that eval operates at global scope rather than within the reviver function's scope. Normally, eval inherits the scope where it is called, but indirect eval as demonstrated (or by assigning eval to a variable before execution) runs at a global level.