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//Objects and Arrays:
 var obj = {key: "value"};
 localStorage.object = JSON.stringify(obj); //Will ignore private members
 obj = JSON.parse(localStorage.object);
//Boolean:
 var bool = false;
 localStorage.bool = bool;
 bool = (localStorage.bool === "true");
//Numbers:
 var num = 42;
 localStorage.num = num;
 num = +localStorage.num; //short for "num = parseFloat(localStorage.num);"
//Dates:
 var date = Date.now();
 localStorage.date = date;
 date = new Date(parseInt(localStorage.date));
//Regular expressions:
 var regex = /^No\.[\d]*$/i; //usage example: "No.42".match(regex);
 localStorage.regex = regex;
 var components = localStorage.regex.match("^/(.*)/([a-z]*)$");
 regex = new RegExp(components[1], components[2]);
//Functions (not recommended):
 function func(){}
 localStorage.func = func;
 eval(localStorage.func); //recreates the function with the name "func"

I do not recommend to store functions because eval() is evil can lead to issues regarding security, optimisation and debugging. In general, eval() should never be used in JavaScript code.

The problem with using JSON.stringify() for storing objects is, that this function can not serialise private members. This issue can be solved by overwriting the .toString() method (which is called implicitly when storing data in web storage):

//Object with private and public members:
 function MyClass(privateContent, publicContent){
 var privateMember = privateContent || "defaultPrivateValue";
 this.publicMember = publicContent || "defaultPublicValue";
 this.toString = function(){
 return '{"private": "' + privateMember + '", "public": "' + this.publicMember + '"}';
 };
 }
 MyClass.fromString = function(serialisedString){
 var properties = JSON.parse(serialisedString || "{}");
 return new MyClass(properties.private, properties.public);
 };
//Storing:
 var obj = new MyClass("invisible", "visible");
 localStorage.object = obj;
//Loading:
 obj = MyClass.fromString(localStorage.object);

var obj = {};
obj["circular"] = obj;
localStorage.object = JSON.stringify(obj); //Fails

In this example, JSON.stringify() will throw a TypeError "Converting circular structure to JSON". If storing circular references should be supported, the second parameter of JSON.stringify() might be used:

var obj = {id: 1, sub: {}};
obj.sub["circular"] = obj;
localStorage.object = JSON.stringify(obj, function(key, value) {
 if(key == 'circular') {
 return "$ref"+value.id+"$";
 } else {
 return value;
 }
});

There are already some question on SO dealing with this problem: Stringify (convert to JSON) a JavaScript object with circular reference

//Objects and Arrays:
 var obj = {key: "value"};
 localStorage.object = JSON.stringify(obj); //Will ignore private members
 obj = JSON.parse(localStorage.object);
//Boolean:
 var bool = false;
 localStorage.bool = bool;
 bool = (localStorage.bool === "true");
//Numbers:
 var num = 42;
 localStorage.num = num;
 num = +localStorage.num; // Short for "num = parseFloat(localStorage.num);"
//Dates:
 var date = Date.now();
 localStorage.date = date;
 date = new Date(parseInt(localStorage.date));
//Regular expressions:
 var regex = /^No\.[\d]*$/i; // Usage example: "No.42".match(regex);
 localStorage.regex = regex;
 var components = localStorage.regex.match("^/(.*)/([a-z]*)$");
 regex = new RegExp(components[1], components[2]);
//Functions (not recommended):
 function func(){}
 localStorage.func = func;
 eval(localStorage.func); // Recreates the function with the name "func"

I do not recommend to store functions, because eval() is evil and can lead to issues regarding security, optimisation and debugging.

In general, eval() should never be used in JavaScript code.

The problem with using JSON.stringify() for storing objects is, that this function can not serialise private members.

This issue can be solved by overwriting the .toString() method (which is called implicitly when storing data in web storage):

//Object with private and public members:
 function MyClass(privateContent, publicContent){
 var privateMember = privateContent || "defaultPrivateValue";
 this.publicMember = publicContent || "defaultPublicValue";
 this.toString = function(){
 return '{"private": "' + privateMember + '", "public": "' + this.publicMember + '"}';
 };
 }
 MyClass.fromString = function(serialisedString){
 var properties = JSON.parse(serialisedString || "{}");
 return new MyClass(properties.private, properties.public);
 };
//Storing:
 var obj = new MyClass("invisible", "visible");
 localStorage.object = obj;
//Loading:
 obj = MyClass.fromString(localStorage.object);

var obj = {};
obj["circular"] = obj;
localStorage.object = JSON.stringify(obj); //Fails

In this example, JSON.stringify() will throw a TypeError "Converting circular structure to JSON".

If storing circular references should be supported, the second parameter of JSON.stringify() might be used:

var obj = {id: 1, sub: {}};
obj.sub["circular"] = obj;
localStorage.object = JSON.stringify(obj, function(key, value) {
 if(key == 'circular') {
 return "$ref" + value.id + "$";
 } else {
 return value;
 }
});

There are already some question on Stack Overflow dealing with this problem: Stringify (convert to JSON) a JavaScript object with circular reference

There are already some question on SO dealing with this problem: Stringify (convert to JSON) a JavaScript object with circular reference

There are already some question on SO dealing with this problem: Stringify (convert to JSON) a JavaScript object with circular reference

It seems that the answers here don't cover all types that are possible in JavaScript, so here are some short examples on how to deal with them correctly (stringify doesn't solve all problems):

Another problem are circular references:

Stringify doesn't solve all problems

It seems that the answers here don't cover all types that are possible in JavaScript, so here are some short examples on how to deal with them correctly:

Private members

Circular references

Another problem stringify can't deal with are circular references: