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Use previous value of "A"

Community Expert ,
Feb 19, 2019 Feb 19, 2019

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Hi JavaScript experts.

I need to use the previous value of "A" in a function but my brain isn't enought logical to find an easy way by itself.

function myFunction(A) {

    // 1. blablabla, use A in one or several lines

    // 2. here I need to keep the value of A for the next time the function will be called

}

Thank you for your help.

TOPICS
Acrobat SDK and JavaScript

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correct answers 1 Correct answer

Community Expert , Feb 20, 2019 Feb 20, 2019

So it's not the previous value of A, it's the one before that...

You can do it like this:

var prevA = [];

function goThere(newA) {

    prevA.push(newA);

    this.pageNum = newA;

}

function goBack() {

    if (prevA.length>=2) this.pageNum = prevA[prevA.length-2];

    else console.println("can't go back.");

}

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LEGEND ,
Feb 19, 2019 Feb 19, 2019

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You can save a value in a variable but (a) don't use "var" and (b) define it OUTSIDE your function first.

Info about variable scope in JavaScript: Demystifying JavaScript Variable Scope and Hoisting

mySavedVariable = -99999999 ;

function myStuff(A)

{

  // do things

  if ( A != mySavedVariable ) { // do things if A is different from last time

  }

  mySavedVariable = A ; // save A for next time

}

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LEGEND ,
Feb 19, 2019 Feb 19, 2019

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Another approach is to use a closure, which avoids the problem of a global variable like TSN suggested from being changed by code elsewhere. This subject can be a bit complicated, but there are plenty of tutorials out there, such as: JavaScript Function Closures

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Community Expert ,
Feb 19, 2019 Feb 19, 2019

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Thank you both but it does not meet my needs, I will try to explain myself better.

In fact there are 2 functions :

function goThere(A) {

this.pageNum = A;

}

//

function goBack() {

this.pageNum = B;

}

Where B is the previous value of A, not the latest value. Otherwise it will goBack on the current page.

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Community Expert ,
Feb 19, 2019 Feb 19, 2019

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Something like this?

var prevA;

function goThere(newA) {

    prevA = newA;

    this.pageNum = newA;

}

function goBack() {

    this.pageNum = prevA;

}

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Community Expert ,
Feb 20, 2019 Feb 20, 2019

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Something like this?

var prevA;

function goThere(newA) {

    prevA = newA;

    this.pageNum = newA;

}

function goBack() {

    this.pageNum = prevA;

}

No. This is the first test I made.

In this case goBack will always go to the current page, since prevA is always equal to newA.

What I want to achieve:

User clic goThere(4) to go to page 4.

User clic goThere(6) to go to page 6.

User clic goThere(9) to go to page 9.

User clics goBack ==> he should go to page 6

I just need one goBack, not several.

(Don't ask me why, but I cannot use app.goBack() for this document.)

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Community Expert ,
Feb 20, 2019 Feb 20, 2019

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So it's not the previous value of A, it's the one before that...

You can do it like this:

var prevA = [];

function goThere(newA) {

    prevA.push(newA);

    this.pageNum = newA;

}

function goBack() {

    if (prevA.length>=2) this.pageNum = prevA[prevA.length-2];

    else console.println("can't go back.");

}

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Community Expert ,
Feb 20, 2019 Feb 20, 2019

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LATEST

So it's not the previous value of A, it's the one before that...

That's what I meant when I wrote "Where B is the previous value of A, not the latest value".

But English is not my native langage.

In any case you are a genius, it works perfectly !

Thank you, and thank you all.

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Community Expert ,
Feb 19, 2019 Feb 19, 2019

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Hi JR, do you want the value of A saved permanently in the PDF, or just for the current session?

The easiest and most straight forward solution is to use a custom document property

Like this

function goThere(newA) {

    this.prevA = newA;

    this.pageNum = newA;

}

Now A is saved in a document level property.

If you want it saved permanently, then use a hidden field.

Cheers,

Thom Parker - Software Developer at PDFScripting
Use the Acrobat JavaScript Reference early and often

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Community Expert ,
Feb 20, 2019 Feb 20, 2019

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Hi JR, do you want the value of A saved permanently in the PDF, or just for the current session?

I want this value to be saved until user go to another page (when the value should be replaced by a newer).

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