save data in a json flie without overwriting existing file in python

i need to add data in an json file without overwriting.

the code am using is:

import json
data=[]
def arr():

x=0

while x<1:

print(x)

x-=1

X.append(x)

data.update(x)

with open(‘x.txt’,‘w’)as outfile:

json.dump(data,outfile)
arr()

print(X)

this one works file.But,while am running this code second time it overwrites the existing values in the text file.help me to solve this code

#json #arrays #python