Baffled by [i]

[Larry Serflaten]

I ran into a program from a novice using a strange syntax that apparently was acceptable.

The program was printing text inside a loop, but used the loop iterator enclosed in brackets

to position the text, such as:

text(list[i], [i], 20);

And oddly enough it works, as in:

var txt = ["A", "B", "C", "D", "E"];

fill(0);
for (var i=0; i<txt.length; i++){
    text(txt[i], 20, [i]);              // what is [i]  ???
    text(i + "  " + [i], 40, [i]);      // clearly not = i,  or is it?
   
}

textAlign(LEFT, TOP);     // something to do with text() ?

for (var j=txt.length; j--;){
    text(txt[j], 200, [j]);
    text(j + "  " + [j], 240, [j]);
}

The output should all be at Y locations of 1-4, but its not.

In the first loop, the text is on a separate line, and in the

second loop, the text is like on separate paragraphs.

I can find no documentation that explains this, does someone have

some insight as to what is going on?

Thanks

LFS

[Element118]

[i] constructs an array with one element. In the text function, I guess the [i] in text(txt[i], 20, [i]); would be converted into a number, and the [i].toString() will be called for i + " " + [i]. The code suggests that the text overlaps with itself.

[Larry Serflaten]

On Saturday, January 16, 2016 at 9:44:39 AM UTC-6, Element118 wrote:

[i] constructs an array with one element.

... 

The code suggests that the text overlaps with itself.

You should try the code and see the results.  I also would expect the text to

overlap itself, but it does not, and that is what is surprising.

Here is the loop:

for (var i=0; i<txt.length; i++){
    text(txt[i], 20, [i]);

}

If you were to unwrap the loop and put in literal values, then it should

unwrap like:

text("A", 20, 0);

text("B", 20, 1);

text("C", 20, 2);

text("D", 20, 3);

That is what I would expect, where the text should overlap.  But the

result looks more like:

text("A", 20, 0);

text("B", 20, 12);

text("C", 20, 24);

text("D", 20, 36);

If you print [i] to try to see where they get their value, it matches the

iterator i, so why doesn't the text overlap?  It is still baffling me....

LFS

 

[Element118]

The same behaviour happens replacing [i] with ""+i. The value of TOP is 101 and the spacing of the text is 100, but I cannot find similar patterns...

[Bob Lyon]

If you look at the implementation of `text`, it splits its first argument into separate lines and invokes the internal function `text$4(lines[count], x, y+yOffset);` In your first loop `yOffset` is inevitably zero, so the value of the last argument to `text$4` is a string that appears to be the user's intent times ten, e.g. '00', '10', '20', '30', '40'.  `text$4` invokes another internal function after manipulating the its arguments -- something like `textInternal(t, x, y-yOnset);` In your first loop, the value of `yOnset` is inevitably zero.  Javascript knows that the operands of subtraction are numbers so it coerces the `y` argument to a number, e.g. the number zero, ten, twenty, thirty, and forty.  And everybody is happy and confused.