Exercises in Chapter 4 of Eloquent Javascript

Chapter4.js

//Ex. 4.2

function range (num) {
    var arr = [];
    if (isNaN(Number(num)))
	alert ("Invalid number");
    else
	for (var i=0;i<num;i++)
	    arr[i]=i;
    return arr;
}
range(5);

//Ex. 4.3

var mack = [];
mack.push("Mack");
mack.push("the");
mack.push("Knife");
show(mack.join(" "));
show(mack.pop());
show(mack);
mack.push("bandit");
mack.push("comes to town.");

/**
js> mack
Mack,the,Knife,bandit,comes to town.
js> mack.join(" ")
Mack the Knife bandit comes to town.
js> mack.join(" ").split(" ")
Mack,the,Knife,bandit,comes,to,town.
*/


//join/split combo do not give back the original array if some of the values originally contained the join string. 

function startsWith (first,second) {
    var chunk = first.slice(0,second.length);
    return chunk == second;
}

/**

js> startsWith("sarah","sa")
true
js> startsWith("sarah", "sasasasa");
false
*/

//Ex. 4.5 
function catNames (paragraph) {
    var lines = paragraph.split("/n");
    var catnames = [];
    for (var i=0;i<lines.length;i++) {
	var colon = lines[i].indexOf(":");
	if (colon >= 0) {// cat names here
	    var names = lines[i].slice(colon+1);
	    var cats = names.split(",");
	    for (var j=0;j<cats.length;j++)
		catnames.push(cats[j]);
	}
    }
    return catnames;
}
    
/**
js> catNames(myparr);
 Doctor Hobbles the 2nd, Noog
*/
     // unfortunately, I get the space before "Doctor".     

     //Ex. 4.6

function extractDate (sentence) {
     var colon = sentence.indexOf(":");
     var beforeColon = sentence.slice(0,colon);
     var extract = beforeColon.split(" ");
     var thedate = extract[1];
     var compDate = thedate.split("/");
     return new Date(compDate[2],compDate[1],compDate[0]);
 }

var mystr = "died 27/04/2006: Black Leclère";
extractDate(mystr);

//Ex 4.7
function between (str, first, second) {
    var index1 = str.indexOf(first);
    var index2 = str.indexOf(second,index1);
    return str.slice(index1+2,index2);

}

/**
js> var mystr = "bu ] boo [ bah ] gzz";
js> 
js> between (mystr, "[ ", " ]");
bah
*/


// looking at the solution, I should have made my solution more general

// Ex. 4.8 


function formatDate(date) {
    var myday = date.getDate();
    if (myday < 10)
	myday = "0" + myday;
    var mymonth = date.getMonth() + 1;
    if (mymonth < 10)
	mymonth = "0" + mymonth;
  return myday + "/" + mymonth +
         "/" + date.getFullYear();
}

// here again, looking at the solution, I feel short of the generalization required in the code 
// where a pad function within the function formatDate would have taken care of the code duplication.
// I'll blame it on too much Java. 

/**
js> print (mydate);
Wed Feb 09 2011 16:36:34 GMT-0500 (EST)
js> formatDate (mydate);
09/02/2011
*/

// Ex. 4.9 
// oldest cat
// Each cat object consists of property/value pair with birth: as a property

	    
function oldestCat (catData) {
    var oldest = "unknown";
    var birthdate = new Date().getTime();
    for (var cat in catData) {
	var catbirth = catData[cat].birth.getTime();
	if (catbirth < birthdate) {
	    oldest = cat;
	    birthdate = catbirth;
	}
    }
    return oldest;
}

// okay, I didn't check to see if the cat was living or not !("death" in cat)
// so I got "Spot" as the oldest cat instead of "Bugeye"

// Ex. 4.10
// Extended range function to have a start-range number

function xRange (start, end) {
    if (arguments.length < 2) {
	end = start;
	start = 0;
    }
    if (start > end) {
	print (end + " not greater than " + start);
	return;
    }

    var arr = [];
    var k = 0;
    for (var i=start;i<end;i++,k++)
	    arr[k]=i;
    return arr;
}

/**
js> xRange(3,8);
3,4,5,6,7
js> xRange(8);
0,1,2,3,4,5,6,7
*/
// okay, looking at the solutions here, I should have used arr.push(i) to dynamically populate the array. No need for this extra k variable. 

// Ex. 4.11

function sum (numList) {
    var sum = 0;
    for (var i=0;i<numList.length;i++)
	sum += numList[i];
    return sum;
}