Array value changes but there is no code that changes that value-CodePudding

I need help to understand this.

var vectX = [];
var esaminatori = [];

... (code omitted)

vectX = ws.getRange(5, 10, 5, 3).getValues();
for (i = 0; i < 5; i  ) {
   if (vectX[i][0] != "") {
     numEsaminatori   ;
     esaminatori[numEsaminatori-1] = vectX[i];
   };
};

... (code omitted)

for (ii = 0; ii < 5; ii   ) {
  vectX[ii][3] = " ";
  for (i = 0; i < numEsaminatori; i   ) {
    if (vectX[ii][0] === esaminatori[i][0]) {
      vectX[ii][3] = esaminatori[i][3];
      i = 6;
    };
  };
};  

ws.getRange(5, 10, 5, 4).setValues(vectX);

The above lines are the only parts of a 230 lines program where appears the array vectX.

Array vectX comes from the spreadsheet and is an array of 5 rows 3 columns, rows may be full of empty, so I copy only the full lines to array esaminatori. In the case I'm testing rows 3 and 5 are empty, rows 1, 2 and 4 have values. So in array esaminatori will be filled rows 0, 1, 2 while in vectX are filled rows 0, 1, 3 and rows 2 and 4 are empty. During the program a new column (index 3) is inserted in array esaminatori, surprisingly the same value in column 3 is added in vectX, but no line of the code makes that. The most incredible is that the value is not inserted randomly, is inserted in the correct [row,column] having in consideration the empty lines.

At the end of the program I want to insert esaminatori column 3 in vectX to write it in the sheet, but not all the lines have values so I initialize the column 3 with a space, otherwise I'll get an error in writing. Now, the strange is that the line that changes the value in vectX[ii][3] automatically changes the corresponding row in esaminatori and lose the content.

So, I could say that in some way the 2 arrays are connected and mirroring themselves.

I have a ghost in my program???

CodePudding user response：

Arrays are assigned by reference not by value. esaminatori[numEsaminatori-1] = vectX[i] assigns the address of the row array of vectX to esaminatori so now vectX and esaminatori share the same address. No ghost.

function test() {
  try {
    let a = [[1,2,3],[4,5,6],[7,8,9]];
    let b = [];
    for( let i=0; i<a.length; i   ) {
      b[i] = a[i];
    }
    console.log("b before:" b);
    for( let i=0; i<b.length; i   ) {
      b[i][0] = b[i][0] 10;
    }
    console.log("b after:" b);
    console.log("a after:" a);
  }
  catch(err) {
    console.log(err)
  }
}

8:56:03 PM  Notice  Execution started
8:56:04 PM  Info    b before:1,2,3,4,5,6,7,8,9
8:56:04 PM  Info    b after:11,2,3,14,5,6,17,8,9
8:56:04 PM  Info    a after:11,2,3,14,5,6,17,8,9
8:56:04 PM  Notice  Execution completed