4 ms·

I'd like to have a guide for writing code that is easily optimized by V8 and similar engines. Having local variables is good, as far as I can tell, but it would

• drivebyacct2 16y ago
  "Having local variables is good" Reading sentences like this scare me because it reminds me that some people don't know what the 'var' keyword means or think it's acceptable to shove everything in window or global.
  • ams6110 16y ago
    Last I read, JavaScript has 2 scopes: function scope, and global scope. Unlike many languages, there is no block scope (e.g. a counter in a for loop).
    • carussell 16y ago
      There is in Mozilla https://developer.mozilla.org/en/New_in_JavaScript_1.7#let_statement https://developer.mozilla.org/en/New_in_JavaScript_1.7#let_s... http://wiki.ecmascript.org/doku.php?id=proposals:block_expressions&s=let http://wiki.ecmascript.org/doku.php?id=proposals:block_expre...
      • solutionyogi 16y ago
        It's definitely not available in current JavaScript interpreter in different browsers.
    • drivebyacct2 16y ago
      I feel dumb now because I fear I don't understand what you mean when you say block scope... for(var i=0; i<3; i++) { console.log(i); } appears to be valid... (or just in Chrome?)
      • aboodman 16y ago
        Valid, just doesn't do what you think. function foo() { var x = 1; if (true) { var x = 2; var y = 3; } console.log(x); console.log(y); } foo(); // 2, 3 (vs 1, undefined if there was block scope)
        • drivebyacct2 16y ago
          Thanks for the explanation!
      • pornel 16y ago
        JS performs "variable hoisting", so your example is interpreted as: function(){ var i; … for(i=0; … It has surprising side effects: alert(i); var i; works and outputs "undefined", which is value of the variable i that is defined. alert(k); var i; This is an error, and will fail to execute because of undefined variable.
    • eru 16y ago
      On the other hand, JavaScript allows you to nest functions, unlike many languages.