为什么在修改值之前将变量赋值给变量

Question

let Text = [];
let textsize = 10;
let Total_Character = 0;
let Ypos = 100;

function setup() {
  createCanvas(400, 400);
}

function keyPressed() {

  //All the characters which I DON'T want in the text, and their keycode

  // 8 = BackSpace, 17 = Control, 13 = Enter(NotDone), 16 = SHIFT, 18 = ALT, 20 = CAPS LOCK, 9 = TAB, 27 = ESCAPE, 45 = INSERT, 46 = DELETE, 33 = PAGE UP, 34 = PAGE DOWN, 36 = HOME, 35 = END, 144 = NUM LOCK, 91 = WINDOWS, 173 = F1, 174 = F2, 175 = F3, 177 = F4, 179 = F5, 176 = F6, 118 = F7, 91 = F8, 38 = UP ARROW, 39 = RIGHT ARROW, 40 = DOWN ARROW, 37 = LEFT ARROW

  //All the Values I don't want in my text writer (Such as "Media Volume Down")
  if (keyCode != 8 && keyCode != 17 && keyCode != 16 && keyCode != 18 && keyCode != 20 && keyCode != 9 && keyCode != 27 && keyCode != 45 && keyCode != 46 && keyCode != 33 && keyCode != 34 && keyCode != 36 && keyCode != 35 && keyCode != 144 && keyCode != 91 && keyCode != 173 && keyCode != 174 && keyCode != 175 && keyCode != 177 && keyCode != 179 && keyCode != 176 && keyCode != 118 && keyCode != 91 && keyCode != 38 && keyCode != 39 && keyCode != 40 && keyCode != 37) {
    //Only true if you press a key that is NOT one of the keycodes listed above, it pushes the key into the Text array (Not to be confused with `text` function)
    Text.push(key)
  }
}

function draw() {
  background(220);

  Total_Character = Text.length;

  //Changes all the different one character strings in the array to one large string
  for (var i = 0; i < Text.length - 1; i++) {
    Text[0] += Text[1];
    Text.splice(1)
  }
  for (var i = 0; i < Text.length; i++) {
    //Displays the text
    textSize(textsize)
    text(Text[i], textWidth(Text[i]) / 2, Ypos);
  }
}

<script src="https://cdn.jsdelivr.net/npm/p5@1.3.1/lib/p5.js"></script>

除非未键入任何内容，否则 Total_Character 变量始终为“1”。这部分是有道理的，因为 Total_Character 是文本的长度，我使文本的长度始终为 1 个大字符串。我需要帮助理解的部分是为什么它是“1”我将 Total_Character 分配给文本的长度 BEFORE 我更改文本的长度，所以不应该不是总字数吗？为什么修改text数组后才定义？

顺便说一句，我在程序中加入了很大一部分，让人们了解我在这里要完成的工作。我本来可以不包含 keyPressed() 下面的代码，但我觉得这样更容易理解我的整个程序，当你运行使用代码片段工具时，它会在片段工具。你可以完全忽略下面的所有内容，因为它不会特别影响这个问题。

Answer 1

您得到的是数组的长度，而不是数组中字符串的长度。

将 Text 的所有元素组合成一个字符串后，就不需要循环遍历它了。只显示 Text[0].

let Text = [];
let textsize = 10;
let Total_Character = 0;
let Ypos = 100;

function setup() {
  createCanvas(400, 400);
}

function keyPressed() {

  //All the characters which I DON'T want in the text, and their keycode

  // 8 = BackSpace, 17 = Control, 13 = Enter(NotDone), 16 = SHIFT, 18 = ALT, 20 = CAPS LOCK, 9 = TAB, 27 = ESCAPE, 45 = INSERT, 46 = DELETE, 33 = PAGE UP, 34 = PAGE DOWN, 36 = HOME, 35 = END, 144 = NUM LOCK, 91 = WINDOWS, 173 = F1, 174 = F2, 175 = F3, 177 = F4, 179 = F5, 176 = F6, 118 = F7, 91 = F8, 38 = UP ARROW, 39 = RIGHT ARROW, 40 = DOWN ARROW, 37 = LEFT ARROW

  //All the Values I don't want in my text writer (Such as "Media Volume Down")
  if (keyCode != 8 && keyCode != 17 && keyCode != 16 && keyCode != 18 && keyCode != 20 && keyCode != 9 && keyCode != 27 && keyCode != 45 && keyCode != 46 && keyCode != 33 && keyCode != 34 && keyCode != 36 && keyCode != 35 && keyCode != 144 && keyCode != 91 && keyCode != 173 && keyCode != 174 && keyCode != 175 && keyCode != 177 && keyCode != 179 && keyCode != 176 && keyCode != 118 && keyCode != 91 && keyCode != 38 && keyCode != 39 && keyCode != 40 && keyCode != 37) {
    //Only true if you press a key that is NOT one of the keycodes listed above, it pushes the key into the Text array (Not to be confused with `text` function)
    Text.push(key)
  }
}

function draw() {
  background(220);

  Total_Character = Text.length;

  //Changes all the different one character strings in the array to one large string
  Text[0] = Text[0].join('');
  Text.splice(1)

  //Displays the text
  textSize(textsize)
  text(Text[0], textWidth(Text[0]) / 2, Ypos);
}

<script src="https://cdn.jsdelivr.net/npm/p5@1.3.1/lib/p5.js"></script>

为什么在修改值之前将变量赋值给变量

Why is a variable being assigned to a value AFTER the value has been modified when I've assigned it before it's been modified

javascript

p5.js