How can terraform parse new changes in the Json file

As part of my work, i would like to parse the data from json and load into another variables. terraform can able to parse the data using from json file with jsondecode function and extracting the required output for the first time.
Next time, when i made changes in the json file, terraform couldnt identify the change as in the state file entry for the json file got already created, in fact json file values got updated.
How can we tell terraform to recheck the json file for new changes?