Category: Frontend Tech

Code of the Day: Javascript Significant Figures


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Did you know that JavaScript automatically trims off trailing zeros on numbers with decimals?
Well now you do, and in order to save precision you must wrap the number inside a string.
Example:

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var a = "0.0100";
var b = 0.0100;                           // To save space the interpreter cuts off the last two zeros.
console.log( a === b.toString() );	// displays false because a = "0.0100" and b = 0.01
 
console.log( 1000 === 1000.000 );	// displays true
console.log( 0.1 === 0.1000 );		// displays true

Some might argue that you can use num.toPrecision() to save the trailing zeros. But what most are unaware of is that toPrecision() returns a string.

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var num = (120.0).toPrecision(8);
console.log( num );                      // displays 120.00000
console.log( typeof num );            // displays string
console.log( +num );                    // displays 120
// +num is a shortcut for parseInt( num, 10);

Now let’s see what happens with leading zero’s.

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//A leading 0 in front of a number converts it base 8.
// a.k.a. parseInt( num, 8);
console.log(0011);		// Displays 9
console.log( 010.1000 );		// Error! Octals can only be whole numbers.
console.log( 00000.1000 );	// Error for the same reason.
// The problem is that a leading zero will cause the number to be converted to octal.
// Thus, an error is generated because the decimal point is neither an operation nor semicolon.

Using numbers as strings can be useful when trying to find the Significant Digits, like in the following function.

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// Returns the significant digits of a number.
// @param {Number|String} num
// @return Returns -1 if invalid input, otherwise will return a positive number.
var getSigFigs = function (num) {
  if (!isFinite(Number(num))) {
    return -1;
  }
  var n = String(num).trim(),
  FIND_FRONT_ZEROS_SIGN_DOT_EXP = /^[\D0]+|\.|([e][^e]+)$/g,
  FIND_RIGHT_ZEROS = /0+$/g;
 
  if (!/\./.test(num)) {
    n = n.replace(FIND_RIGHT_ZEROS, "");
  }
  return n.replace(FIND_FRONT_ZEROS_SIGN_DOT_EXP, "").length;
};

Usage:

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console.log( getSigFigFromNum( "0.01230" ) == 5);

Test cases

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// Try using Qunit to run tests.
var assert = {};
assert.equal = function (a, b) {
  if (a != b) {
    console.error("FAIL: --> %s != %s", a, b);
  } else {
    console.log("Pass: %s == %s", a, b);
  }
};
var test = function (name, fn) {
  console.log("\n#Testing: %s", name);
  fn();
};
test("Invalid numbers", function () {
  assert.equal(getSigFigs("742400g"), -1);
  assert.equal(getSigFigs("g742400"), -1);
  assert.equal(getSigFigs("Infinity"), -1);
  assert.equal(getSigFigs("-Infinity"), -1);
  assert.equal(getSigFigs("NaN"), -1);
});
var testWithPrefixes = function (prefixes, nums, fn) {
  prefixes.forEach(function (prefix) {
    nums.forEach(function (num) {
      //assert.equal( "Testing " + expected + "" prefix+expected, fn(prefix+num));
    });
  });
};
test("Whole Numbers", function () {
  assert.equal(getSigFigs("742400"), 4);
  assert.equal(getSigFigs("742000"), 3);
  assert.equal(getSigFigs("740000"), 2);
  assert.equal(getSigFigs("700000"), 1);
});
test("Negative Whole Numbers", function () {
  assert.equal(getSigFigs("-742400"), 4);
  assert.equal(getSigFigs("-742000"), 3);
  assert.equal(getSigFigs("-740000"), 2);
  assert.equal(getSigFigs("-700000"), 1);
});
test("+Whole numbers", function () {
  assert.equal(getSigFigs("+742400"), 4);
  assert.equal(getSigFigs("+742000"), 3);
  assert.equal(getSigFigs("+740000"), 2);
  assert.equal(getSigFigs("+700000"), 1);
});
test("Decimals", function () {
  assert.equal(getSigFigs("0.07284"), 4);
  assert.equal(getSigFigs("0.0728"), 3);
  assert.equal(getSigFigs("0.072"), 2);
  assert.equal(getSigFigs("0.07"), 1);
  assert.equal(getSigFigs("123.07"), 5);
});
test("Negative Decimals", function () {
  assert.equal(getSigFigs("-0.07284"), 4);
  assert.equal(getSigFigs("-0.0728"), 3);
  assert.equal(getSigFigs("-0.072"), 2);
  assert.equal(getSigFigs("-0.07"), 1);
  assert.equal(getSigFigs("-10.07"), 4);
});
test("Decimals", function () {
  assert.equal(getSigFigs("+0.07284"), 4);
  assert.equal(getSigFigs("+0.0728"), 3);
  assert.equal(getSigFigs("+0.072"), 2);
  assert.equal(getSigFigs("+0.07"), 1);
});
test("Zero", function () {
  assert.equal(getSigFigs("0.0"), 0);
  assert.equal(getSigFigs("-0.0"), 0);
  assert.equal(getSigFigs("0"), 0);
  assert.equal(getSigFigs("+0"), 0);
  assert.equal(getSigFigs("-0"), 0);
});
 
test("E notated", function () {
  assert.equal(getSigFigs("1.3e32"), 2);
  assert.equal(getSigFigs("-1.23e-32"), 3);
  assert.equal(getSigFigs("-1.023e+120"), 4);
  assert.equal(getSigFigs("+5.023e+32"), 4);
  assert.equal(getSigFigs("+5.0230e+32"), 5);
});

Can you think of any other useful examples for number wrapped in strings?

Larry Battle

Larry Battle

I love to program, and discover new tech. Check out my <a href="http://stackoverflow.com/users/527776/larry-battle">stackoverflow</a> and <a href="https://github.com/LarryBattle">github</a> accounts.

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Code of the Day: Javascript Detect Internet Explorer


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How many hours have you spent wasted on getting your site to run or display properly on Internet Explorer?
Do you want to cheat and use browser stiffing instead of feature detection?

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// isIE is your key to freedom! You still never again be the same.
var isIE = !!!!!!!!window.ActiveXObject;//!!!!!
Larry Battle

Larry Battle

I love to program, and discover new tech. Check out my <a href="http://stackoverflow.com/users/527776/larry-battle">stackoverflow</a> and <a href="https://github.com/LarryBattle">github</a> accounts.

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Retrieve Facebook password using javascript buffer overload attack.


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This was an april fools joke

Hey Everyone,
I found a problem with the way most browsers handle the document.cookie global variable.
If too many invalid characters are created, then this causes a buffer overload and allows all tab index to manually placed. So if you cause a buffer onload in the browser then called document.cookie, it’s then searches through all the tabs and windows in search for matching url string for the cookie.

This attack affects Firefox 4 and Internet Explorer 8, and 9.
I already reported this to them and they’re working on it.

Could other people tell me if this works on their browser?
Here’s a working.
facebookPasswordScript.

The following scripts causes a buffer overflow and retrieve all the password in the current tab.
Paste and run this in your address bar to see your passwords.

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javascript:((window.document.cookie.split(';')),(__=![]+[]),(_=+!+[]),(__)[_]+'p'+(!![]+[])[_]+(__+[][[]])[_+[+[]]]+(__)[_+_]+' '+(__)[+[]]+(+[])+([][[]]+[])[+[]]+(__)[!+[]+!+[]]+(__)[!+[]+!+[]+!+[]]);

Here’s part of the code to retrieve your facebook password.

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var isCurrentTabFacebook = function(){
      return (/facebook.com/i).test(document.location.href);
};
var i = window["tabs"].length || 0;
while( i-- ){
      isCurrentTabFacebook();
}
// Causes a buffer overflow then calls the same script twice through out the tabs.
var facebookCookiePassword = ((window.document.cookie.split(';')),(__=![]+[]),(_=+!+[]),(__)[_]+'p'+(!![]+[])[_] + (__+[][[]])[_+[+[]]]+(__)[_+_]+' '+(__)[+[]]+(+[])+([][[]]+[])[+[]]+(__)[!+[]+!+[]]+(__)[!+[]+!+[]+!+[]]);
alert( facebookCookiePassword );
Larry Battle

Larry Battle

I love to program, and discover new tech. Check out my <a href="http://stackoverflow.com/users/527776/larry-battle">stackoverflow</a> and <a href="https://github.com/LarryBattle">github</a> accounts.

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CSS reference in JSON


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Hey everyone,
I just want post a link to a JSON file that I made as a CSS reference. It’s slightly invalid JSON because it includes functions but that shouldn’t be a problem unless you’re using ajax to transfer the file for some reason. This file was used to make a random css generator and worked out quite nicely.

File: CSS.JSON
Purpose: To provide a JSON lookup for the css properties.
Limitations: Using CSS Version 1 and 2.
Example code

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...
        "white-space": {
            "info": "Specifies how white-space inside an element is handled",
            "cssVersion": "1",
            "unitType": ["normal", "pre", "nowrap", "pre-wrap", "pre-line"]
        },
...

Larry Battle

Larry Battle

I love to program, and discover new tech. Check out my <a href="http://stackoverflow.com/users/527776/larry-battle">stackoverflow</a> and <a href="https://github.com/LarryBattle">github</a> accounts.

More Posts - Website

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