How to handle potentially "false" inputs in JSON? Discussion of alternatives

Question

Let's say, I'm not sure if the selected authorities exist (but if they exist, I want them to be selected). If there are no selected authorities, I want jQuery to select the authorities regardless of whether they are selected (actually, this means retrieving the value of the hidden input). My idea of ​​using JS's "true value"/"false value" concept to handle this situation is: letuser={id:$(this).find('[name=id]').val(),username :$(thi

P粉818306280 · Answer

The problem is that if the selector doesn't find any matches, .val() returns undefined, while JSON.parse(undefined) throws an exception .

Execute the fallback in the parameter list of JSON.parse() so that you will parse any value that is successfully obtained.

authorities: JSON.parse($(this).find('[name=authorities]:checked').val() || 
                        $(this).find('[name=authorities]:first').val())

P粉561323975 · Answer

Depending on your use case, you have several options:

You can combine JSON.parse like this. This will make it fall back to other strings before parsing, so it won't error if the first value is undefined. However, this will result in an error if both values are undefined or one of them is invalid JSON.

JSON.parse($(this).find('[name=authorities]:checked').val()) || $(this).find('[name=authorities]').val());

If you know that the values are either valid JSON or undefined, you can fall back to null. null is a valid JSON value and can be parsed. However, if any of the values are invalid JSON, an error will still occur.

JSON.parse($(this).find('[name=authorities]:checked').val()) || $(this).find('[name=authorities]').val() || null);

If there is a chance that either value is invalid JSON, you can surround it in a try/catch block. This way, even if it is invalid, no error will be thrown. This is the safest option and will never go wrong.

// Helper to make it easier to do this inline
function safeJsonParse(string) {
  try {
    return JSON.parse(string);
  } catch {
    // JSON is invalid. Will implicitly return undefined.
  }
}

safeJsonParse($(this).find('[name=authorities]:checked').val()) || safeJsonParse($(this).find('[name=authorities]').val())

John	U.S. Department of Energy	IT	john_d@gmail.com
simple	U.S. Department of Energy	human Resources	jane_d@gmail.com
${$(this).find('[name=name]').val()}	${$(this).find('[name=last-name]').val()}	${$(this).find('[name=department]').val()}	${$(this).find('[name=email]').val() \|\| 'Not applicable'}

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