As some of you might know, JavaScript is only able to handle integers up to 53-bit in size. This post, Working with large integers in JavaScript (which is a part of Numbers series) does a great job at explaining general concepts on dealing with large numbers in JS.
I had to do some research on the topic when I was re-writing some JavaScript code responsible for handling Twitter search in Storify editor: we had tweet duplicates in results! In this article, Working with Timelines, Twitter official documentation says:
Environments where a Tweet ID cannot be represented as an integer with 64 bits of precision (such as JavaScript) should skip this step.
So true, because id and id_str fields in a Twitter API response were different. Apparently, JavaScript engine just “rounds” inappropriately large numbers. :-( The task was complicated by the fact that I needed to subtract 1 from the last tweet’s ID to prevent its reappearance in a second search response. After the subtraction I could have easily passed the value to max_id parameter of Twitter API.
I’ve come across different solutions, but decided to write my own function which is simple to understand and not heavy on resources. Here is a script to decrease tweet ID which is a 64-bit number in JavaScript without libraries or recursion, to use with max_id or since_id in Twitter API:
function decStrNum (n) {
n = n.toString();
var result=n;
var i=n.length-1;
while (i>-1) {
if (n[i]==="0") {
result=result.substring(0,i)+"9"+result.substring(i+1);
i --;
}
else {
result=result.substring(0,i)+(parseInt(n[i],10)-1).toString()+result.substring(i+1);
return result;
}
}
return result;
}To check if it works, you can run these logs:
console.log("290904187124985850");
console.log(decStrNum("290904187124985850"));
console.log("290904187124985851");
console.log(decStrNum("290904187124985851"));
console.log("290904187124985800");
console.log(decStrNum("290904187124985800"));
console.log("000000000000000001");
console.log(decStrNum("0000000000000000001"));Alternative solution which I’ve found in a StackOverflow question was suggested by Bob Lauer, but it involves recursion and IMHO is more complicated:
function decrementHugeNumberBy1(n) {
// make sure s is a string, as we can't do math on numbers over a certain size
n = n.toString();
var allButLast = n.substr(0, n.length - 1);
var lastNumber = n.substr(n.length - 1);
if (lastNumber === "0") {
return decrementHugeNumberBy1(allButLast) + "9";
}
else {
var finalResult = allButLast + (parseInt(lastNumber, 10) - 1).toString();
return trimLeft(finalResult, "0");
}
}
function trimLeft(s, c) {
var i = 0;
while (i < s.length && s[i] === c) {
i++;
}
return s.substring(i);
}Now, if you’re the type of person who likes to shoot sparrows with a howitzer, there are full-blown libraries to handle operations on large numbers in JavaScript; just to name a few: BigInteger, js-numbers and javascript-bignum.
