I was tasked by my professor to make a simple Javascript program that displays simple math problems and their answers in a two dimensional table using a random number. Previously he gave us the example of using a function to write into a table like this:
function RandomGen() {
Random = math.floor(Math.random()*60);
document.writeln("<th>");
document.writeln(Random);
document.writeln("</th>");
}
RandomGen();
In order to use an array, can I do this?
var RandomArray [
RandomGen(),
second_function(),
third_function(),
forth_function(),
]
RandomArray[0];
How do I append the functions together to write into a table?
You almost got it. The correct syntax is:
var randomArray = [
RandomGen,
second_function,
third_function,
forth_function
];
randomArray[0](); // this calls RandomGen
randomArray[1](); // this calls second_function
Remember the basic syntax rules:
A function name with no paranthesis is a function reference. It behaves just like any reference and so can be treated as a variable. Which means you can assign it to another variable, pass it into another function and as the example above stuff it into an array.
Adding paranthesis () to a function reference causes the function to be called. It doesn't matter if the function reference is a plain old function name or stored in another variable or stored in an array.
You can store the function in a variable, then put the variables in an array, and then access them from the array to call them.
var add = function(x,y){ return x + y; };
var multiply = function(x,y){ return x * y; };
var maths = [];
maths.push(add);
maths.push(multiply);
maths[0](1,2);//3
maths[1](3,4);//12
Conversely, you could do this with an object.
var maths = {};
maths.add = function(x,y){ return x + y; };
var four = maths.add(1,3);
Obviously you will have to modify these to match your exact situation.
Related
I have tried everything and I can not split a PHP variable into two parts so I can insert them into two input fields. I have read numerous topics here and I don't see the problem...
This peace of code gives me a result that php variable is inserted into a wanted filed.
Lets say the PHP variable is data1-data2:
document.hiderad.selectstate.onchange = updateText;
function updateText() {
var str = document.hiderad.selectstate;
document.hiderad.opis.value = str.value;
}
Code above inserted data1-data2 into wanted HTML input.
And soon as i try to split it i get undefined warning. I have tried 7 different things to approach this problem so i want even list all the versions I tried. Can someone please help?
document.hiderad.selectstate.onchange = updateText;
function updateText() {
var str = document.hiderad.selectstate;
var array = str.toString().split('-');
a = array[0], b = array[1];
document.hiderad.opis.value = a.value;
document.hiderad.iznos.value = b.value;
}
Code above gives me b undefined if i remove last line i get a undefined.
You shouldn't be using a.value and b.value, that's for getting the value of an input field, not a string. You should use that to get the value of the selectstate input.
Also, always declare local variables unless you have a specific reason to assign global variables.
function updateText() {
var str = document.hiderad.selectstate;
var array = str.value.split('-');
var a = array[0], b = array[1];
document.hiderad.opis.value = a;
document.hiderad.iznos.value = b;
}
I am trying to pass a string variable and two arrays to a global function. Something like this:
function send_times_to_device(stop_name, times, headsigns) {
// function code here
}
Later in code:
...
var stop_name = "temp";
var times = new Array(json.length);
var headsigns = new Array(json.length);
...
if(times.length < 6){
send_times_to_device(stop_name, times, headsigns);
}
...
How would I do this correctly in Javascript?
Thanks in advance!
EDIT:
You guys were right, there was an error elsewhere in my code, this works!
new Array(n), creates an array with n undefined entries in it.
If you want to create an array with an integer value as the first entry use :
function send_times_to_device(stop_name, times, headsigns) {
// function code here
console.log(stop_name);
console.log(times);
console.log(headsigns);
}
var stop_name = "temp";
var times = [json.length];
var headsigns = [json.length];
send_times_to_device(stop_name, times, headsigns);
I'm trying to create an array of objects with an init method, and when I push an object into an array, it should push another object into the array, while keeping track of the length of the array.. The problem is that it doesn't update the length of the array until all the objects have been added, so when each object tries to grab the length, they all get 0.
How can I have it update the length in this process?
here's the jfiddle: http://jsfiddle.net/bg3Vg/13/
As you can see it gives a message showing that the grouptotal is 5, but it seems as if the total counts up from the last pushed object to the first.. I need it to work in the correct order so that the last pushed object can retrieve the correct length.
var colorGroup = [];
var grouptotal = 0;
colorGroup.push(new groupdata(0) );
alert(grouptotal+","+colorGroup[colorGroup.length-1].parent);
function groupdata(parent) {
this.parent = parent;
this.refnum;
this.init = function()
{
grouptotal++;
this.refnum = colorGroup.length;
if(grouptotal<5)colorGroup.push(new groupdata( this.refnum ) );
}
this.init();
}
edit:
ok, I found a way to solve my problem I think. Let me know how horrid this solution is..http://jsfiddle.net/EqAqv/1/
var colorGroup = [];
var grouptotal = 0;
var colorGroupWait = [];
colorGroup.push(new groupdata(0) );
while(colorGroupWait.length>0){
var newcolorGroup = colorGroupWait.shift();
colorGroup.push(new groupdata(newcolorGroup) );
}
alert(grouptotal+","+colorGroup[colorGroup.length-1].parent);
alert(grouptotal+","+colorGroup[colorGroup.length-2].parent);
function groupdata(parent) {
this.parent = parent;
this.refnum;
this.init = function()
{
grouptotal++;
this.refnum = colorGroup.length;
if(colorGroup.length<5)colorGroupWait.unshift( this.refnum );
}
this.init();
}
JavaScript arrays do update the length property as soon as you push something on to them. The problem is that you're recursively calling the constructor, so the statement this.refnum = colorGroup.length is getting executed for each initialization BEFORE any push occurs.
In other words, JavaScript is working as expected.
Is there any particular reason you are doing it in this convoluted manner? It be more straightforward (and achieve the result you're looking for) if you just did it like this:
for(grouptotal=0; grouptotal<5; grouptotal++){
colorGroup.push( new groupdata(grouptotal) );
}
Also, it is convention in JavaScript to name object constructors with a capital letter. So, while groupdata is not invalid syntax, it is confusing: you should consider naming it Groupdata.
#EthanBrown has already pointed out the problems. Here is a solution that puts all the logic in the constructor, and avoids the problem of pushing the instance after having it created from a wrong number.
function GroupData(parentnum) {
this.parentnum = parentnum;
this.refnum = GroupData.colorGroup.length;
GroupData.colorGroup.push(this);
if (GroupData.colorGroup.length < 5)
new GroupData(this.refnum);
}
GroupData.colorGroup = [];
var root = new GroupData(0);
alert(GroupData.colorGroup.length+", "
+GroupData.colorGroup[GroupData.colorGroup.length-1].parentnum);
I am trying to break a javascript object in to small array so that I can easily access the innerlevel data whenever I needed.
I have used recursive function to access all nodes inside json, using the program
http://jsfiddle.net/SvMUN/1/
What I am trying to do here is that I want to store these in to a separate array so that I cn access it like
newArray.Microsoft= MSFT, Microsoft;
newArray.Intel Corp=(INTC, Fortune 500);
newArray.Japan=Japan
newArray.Bernanke=Bernanke;
Depth of each array are different, so the ones with single level can use the same name like I ve shown in the example Bernanke. Is it possible to do it this way?
No, you reduce the Facets to a string named html - but you want an object.
function generateList(facets) {
var map = {};
(function recurse(arr) {
var join = [];
for (var i=0; i<arr.length; i++) {
var current = arr[i].term; // every object must have one!
current = current.replace(/ /g, "_");
join.push(current); // only on lowest level?
if (current in arr[i])
map[current] = recurse(arr[i][current]);
}
return join;
})(facets)
return map;
}
Demo on jsfiddle.net
To get the one-level-data, you could just add this else-statement after the if:
else
map[current] = [ current ]; // create Array manually
Altough I don't think the result (demo) makes much sense then.
I currently have a block like this defining some vars
var slider_1 = document.querySelector('#slider_1');
var slider_2 = document.querySelector('#slider_2');
...
And func's that take ID's like this:
function updateFromInput(id){
if(id==1){
var x = input_1.value*1;
x = Math.round((x*ratio)-offset);
slider_1.x.baseVal.value = x/scale;
}else if(id==2){
var x = input_2.value*1;
x = Math.round((x*ratio)-offset);
slider_2.x.baseVal.value = x/scale;
}
};
I am trying to refactor a bit.
I'm thinking that if I could, instead, instantiate my vars with dots rather than underscores like
var slider.1 = document.querySelector('#slider_1');
var slider.2 = document.querySelector('#slider_2');
then I'd be able to better utilize the ID already getting passed into my func's and eliminate tons of duplication.
I was hoping to simplify my funcs with something like a single call for slider.id.x.baseVal.value = x/scale; rather than having to have that code in each of the IF/ELSE conditions.
When I try that though, I get an error saying " Uncaught SyntaxError: Unexpected number ".
How should this be done?
You can't use a plain numeric key in an object.
You can do this, though:
var slider = {}; // or = [], if array syntax is more appropriate
slider[1] = ...
slider[2] = ...
Furthermore, the syntax you suggested isn't allowed if the key is actually a variable rather than a literal token.
In your example slider.id actually refers to the object with literal key id, not whatever value the variable id happens to have.
You have to put the variable inside square brackets, i.e. slider[id], so your function would be written thus:
function updateFromInput(id){
var x = +input[id].value;
x = Math.round((x*ratio)-offset);
slider[id].x.baseVal.value = x/scale;
};
You can't. The . is an invalid character for a variable identifier.
You can use it in object properties though.
var sliders = {
"slider.1": document.querySelector('#slider_1'),
"slider.2": document.querySelector('#slider_2')
};
Then use the square bracket version of the member operator to access the property.
alert( sliders["slider.1"].id );