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javascriptarraysstringreplacestartswith

Change the string and replace it in the specific index that I search for it and make new string

I have a SDP file and I convert it to string like bellow:

v=0
o=- 1443716955 1443716955 IN IP4 10.20.130.110
m=video 20000 RTP/AVP 96 // <== this line 
c=IN IP4 239.0.1.2/64
a=source-filter: incl IN IP4 239.0.1.2 192.168.0.1
a=rtpmap:96 raw/90000
a=mid:primary
m=video 20000 RTP/AVP 96 // <== this line 
c=IN IP4 239.0.1.3/64
a=source-filter: incl IN IP4 239.0.1.3 192.168.0.1

And in this line " m=video 20000 RTP/AVP 96 " I want to change '20000' to '4321',I wrote this bellow code: 

 let fileds= inputString .split(/\s+/);
    for(const field of fields) {
     if(field === "m=video") {

      }
     if (field === "m=audio") {
          var myflag = "au";
     }
    }

and above ode give me this bellow result:

m=video 4321 RTP/AVP 96
m=video 4321 RTP/AVP 96

I just want change them and replace to the string(like new string),Imagine I need result like bellow:

v=0
o=- 1443716955 1443716955 IN IP4 10.20.130.110
m=video 4321 RTP/AVP 96 // <== this line
c=IN IP4 239.0.1.2/64
a=source-filter: incl IN IP4 239.0.1.2 192.168.0.1
a=rtpmap:96 raw/90000
a=mid:primary
m=video 4321 RTP/AVP 96 //<== this line
c=IN IP4 239.0.1.3/64
a=source-filter: incl IN IP4 239.0.1.3 192.168.0.1

I totally new in java script, How I can replace it? because maybe I have another string with different "m=video" index in here 'm' in line 2 maybe in next string "m=video" on line 3 or 4.

Can I use ' string.startswith('m=video') ' and where I this code it true replace it with what I got it

EX : m=video 4321 RTP/AVP 96

Solution

  • I have an example:

    Either simply using replace all inputString.replace(/m=video 20000/g, "m=video 4321"), where the g in /m=video 20000/g means replace globally (i.e. replace all).

    Or we can map over each line and replace each line with stringArr.map(str => str.replace(/m=video 20000/, "m=video 4321"))

    To make it dynamic (i.e. allow other numbers other than 20000) we can create a RegExp:

    const inputNumberString = '20000'; //can be changed
const regex = new RegExp('m=video ' + inputNumberString, 'g');
const stringReplacedAll = inputString.replace(regex, "m=video 4321")

    Or if the same pattern is always present but different numbers and you want to match any numbers you can use a RegExp pattern match like:

    const inputPattern= /m=video \d{5}/g;
const stringReplacedAll = inputString.replace(inputPattern, "m=video 4321")

    To change other parts of the string like the IP, do something like this:

    const inputPattern= /m=video \d{5}/g;
const ipPattern = /c=IN IP4 \d{3}.\d.\d.\d\/\d{2}/g;
const stringReplacedAll = inputString
                    .replace(inputPattern, "m=video 4321")
                    .replace(ipPattern, "c=IN IP4 123.0.1.1/88");

    Which matches any 5 digit number after 'm=video ';

    const inputString = 
`v=0
o=- 1443716955 1443716955 IN IP4 10.20.130.110
m=video 20000 RTP/AVP 96 // <== this line 
c=IN IP4 239.0.1.2/64
a=source-filter: incl IN IP4 239.0.1.2 192.168.0.1
a=rtpmap:96 raw/90000
a=mid:primary
m=video 20000 RTP/AVP 96 // <== this line 
c=IN IP4 239.0.1.3/64
a=source-filter: incl IN IP4 239.0.1.3 192.168.0.1`;

const inputNumberString = '20000';
const inputPattern= /m=video \d{5}/g;
const ipPattern = /c=IN IP4 \d{3}.\d.\d.\d\/\d{2}/g;
const regex = new RegExp('m=video ' + inputNumberString, 'g');
const stringReplacedAll = inputString.replace(inputPattern, "m=video 4321").replace(ipPattern, "c=IN IP4 123.0.1.1/88");

console.log(stringReplacedAll);

//OR you can do it with array and map
const stringArr = inputString.split('\n');
const stringReplacedMap = stringArr.map(str => str.replace(/m=video 20000/, "m=video 4321")).join('\n');

//console.log(stringReplacedMap);