JavaScript Type Conversions

JavaScript Type Conversions and some explanations to the Gary Bernhardt's wat lighting talk

Transcript

1. JavaScript Type Conversions
2. JavaScript Primitives yes, js has primitives
3. 1. undefined 2. null 3. number 4. string 5. boolean
4. 1. undefined 2. null yep, is not an object 3. number 4. string 5. boolean
5. JavaScript Binary Operators we are going to address only - and +
6. On doubt check the spec
7. http://www.ecma-international.org/ecma-262/5.1/#sec-11.6.1 http://www.ecma-international.org/ecma-262/5.1/#sec-11.6.2
8. + Operator
9. If lprim or rprim are strings, then concatenate lprim and rprim and return the result
10. - Operator
11. ToNumber(lprim) - ToNumber(rprim)
12. Examples
13. var a, b; a = "bla"; b = "ble"; a + b; //=> "blable" a - b; //=> "NaN" a = "5"; b = "4"; a + b; //=> "54" a - b; //=> 1
14. var obj = { valueOf: function valueOf() { console.log("valueOf"); return {}; // not a primitive }, toString: function toString() { console.log("toString"); return {}; // not a primitive } }; obj - 1; // valueOf // toString // error obj + 1; // valueOf // toString // error
15. var func = function () { console.log('exec'); return { valueOf: function valueOf() { console.log("valueOf"); return {}; // not a primitive }, toString: function toString() { console.log("toString"); return {}; // not a primitive } }; }; func() + 1; // exec // valueOf // toString // error
16. {} + [] //=> +[] == 0 [] + {} //=> '' + '[object Object]' == '[object Object]' [] - {} //=> 0 - NaN == NaN {} - [] //=> -[] == -0
18. WAT https://www.destroyallsoftware.com/talks/wat