# My binary search algorithm implementation in JavaScript

I have implemented binary search algorithm in JavaScript:

var myArray = [],
searchNum = undefined;

// below function is used to capture the
// commandline parameters for array and the
// number to be searched
(function(){
process.argv.forEach(function (val, index, array) {
var idx = 0, ar = undefined;

try{

// get the commandline argument for
// array values
if(index === 2){
myArray = myArray.concat(val.split(",").map(function(num){
return parseInt(num);
}));
}

// third index is the number to be searched.
if(index === 3){
searchNum = parseInt(val)
}

}catch(e){
console.log(e)
}

});
})();

console.log(" SEARCH NUMBER ",searchNum," in array ",myArray);

console.log(binary_search(myArray,searchNum,0,myArray.length));

function binary_search(numberArray, numberToSearch, lowIndex, maxIndex){
var totalLength = maxIndex - lowIndex;

var midIndex = parseInt(totalLength/2),
str = "";

/*
If Lower Index is equal to Higher Index,
a collision in pointers and hence return
as 'Can't be found'
*/
if(lowIndex === maxIndex){
return "can't be found";
}

/*
setting the actual middle index
by adding the computed middle index with lower index.
*/
midIndex = lowIndex + midIndex;

// if number found
if(numberArray[midIndex] === numberToSearch){

str = " Number "+numberToSearch+" found at position "+midIndex;

return str;

// if number in middle index is less than the number to be searched
// set the lower Index to new value i.e. a index position next higher to
// middle Index
}else if(numberArray[midIndex] < numberToSearch){

lowIndex = midIndex + 1;

// number to be searched is less than the number present at middle Index
// set new maxIndex value i.e. index which is previous position to the
// middle index
}else if(numberArray[midIndex] > numberToSearch){

maxIndex = midIndex;

}else{

return "can't be found";

}

return binary_search(numberArray, numberToSearch, lowIndex, maxIndex);
} // end of method binary_search


When I run the above code the output is as follows,

E:\RahulShivsharan\MyPractise\DesignPatternsInJavaScript>node binarySearch.js 12,34,56,78,90 24
SEARCH NUMBER  24  in array  [ 12, 34, 56, 78, 90 ]
can't be found

E:\RahulShivsharan\MyPractise\DesignPatternsInJavaScript>node binarySearch.js 12,34,56,78,90 34
SEARCH NUMBER  34  in array  [ 12, 34, 56, 78, 90 ]
Number 34 found at position 1


Can you please review my code and please suggest me if there is any room for further improvement.

### Parsing command line arguments

I mentioned this in a previous review, it seems I wasn't specific enough, but this is an inefficient and unnatural way to parse command line arguments:

    process.argv.forEach(function (val, index, array) {
var idx = 0, ar = undefined;

try{

// get the commandline argument for
// array values
if(index === 2){
myArray = myArray.concat(val.split(",").map(function(num){
return parseInt(num);
}));
}

// third index is the number to be searched.
if(index === 3){
searchNum = parseInt(val)
}

}catch(e){
console.log(e)
}

});


What's wrong with it?

• For each index 0, 1, 2, 3, the loop compares the index against 2 and 3 repeatedly
• If there are not enough arguments, the loop should not even begin
• The command line parsing logic fails its purpose by not failing in case the arguments are invalid

The natural way to parse would be:

• Check process.argv.length and fail if invalid
• Check the type of each argument and fail if invalid

Consider this alternative, no looping, nice and simple:

function parseArgs(prog, argv) {
if (argv.length != 2) {
throw usage: node \${prog} NUMS_CSV NUM;
}

function validInt(s) {
var num = parseInt(s, 10);
if (isNaN(num)) {
throw "Not a valid number: " + s;
}
return num;
}

return {
nums: argv.split(',').map(validInt),
target: validInt(argv)
};
}

var args = parseArgs(process.argv, process.argv.slice(2));


### Parsing integers

When using parseInt, it's recommended to specify the radix parameter, because although base 10 is a common default, it's not guaranteed across different implementations. So to parse base 10 numbers, write parseInt(x, 10) instead of parseInt(x).

### API design

The binary_search function searches for an element and returns two kinds of strings as result:

• can't be found
• Number N found at position X

This is very limiting. It would be better to have binary_search return an index or -1 if not found, and move the logic of formatting a string result into a dedicated function.

• Why do you recommend specifying the radix 10 for parseInt when that is the default? – kamoroso94 Jul 10 '17 at 12:26
• @kamoroso94 thanks for pointing out, I clarified. According this page, the default is not always 10, that's why it's good to write explicitly always. – janos Jul 10 '17 at 12:33