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Pergunta 21. What are Math routines in Javascript?

the Math object contains functions and constants

Math.sqrt
Math.pow
Math.abs
Math.max
Math.min
Math.floor
Math.ceil
Math.round

Math.PI
Math.E

Math.random function returns number in [0..1)

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Pergunta 22. Write a javascript to get difference between two dates.

now = new Date();
newYear = new Date(2004,0,1);

secs = Math.round((now-newYear)/1000);

days = Math.floor(secs / 86400);
secs = days*86400;
hours = Math.floor(secs / 3600);
secs = hours*3600;
minutes = Math.floor(secs / 60);
secs = minutes*60

document.write(days + " days, " +
hours + " hours, " +
minutes + " minutes, and " +
secs + " seconds.");

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Pergunta 23. What about Navigator object?

navigator.appName property that gives the browser name.
navigator.appVersion property that gives the browser version.
navigator.userAgent property that gives the browser related information.

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Pergunta 24. What is User-Defined class in Javascript?

can define new classes, but the notation is awkward
simply define a function that serves as a constructor
specify data fields & methods using this

no data hiding: can't protect data or methods

function Die(sides)
{
this.numSides = sides;
this.numRolls = 0;
this.Roll = Roll;
}

function Roll()
{
this.numRolls++;
return Math.floor(Math.random()*this.numSides) + 1;
}

die6 = new Die(6);
die8 = new Die(8);

roll6 = -1; // dummy value to start loop
roll8 = -2; // dummy value to start loop
while (roll6 != roll8) {
roll6 = die6.Roll();
roll8 = die8.Roll();

document.write("6-sided: " + roll6 +
" " +
"8-sided: " + roll8 + "
");
}

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Pergunta 25. Few events in Javascript.

onsubmit - call when submit button is clicked
onclick - call when this button is clicked
onreset - call when the reset button is clicked
onload - call after page loads
onmouseover - call when mouse pointer enters image area
onmouseout - call when mouse pointer leaves image area
onfocus - call when control receives focus
onblur - call when a control loses focus
onchange - call when a control loses focus and the value of its contents has changed
onunload – call when a page is closed

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