Angular ngrx: check is field exists in object

Question

I'm sorry if it's a duplication of any question, however, I can't find a solution to my problem.

I have a selector that getting a big object with a big nesting. And I need to return some value from it. How can I check is fields exist to prevent crashing?

export const getSingleValue = createSelector(
    getEntities,
    (entities) => entities
        .map(item => {
            // need to check is field and oneMoreField, etc. exist
           return item.field.oneMoreField.andMoreField.andHereIs.value || null; 
        })
);

The plan B - wrap returning to try-catch but I think it's not a good option.

score 0 · Accepted Answer · answered Dec 17 '18 at 09:26

Typescript doesn't support an Elvis operator out of the box.

So some of the options you have:

Manually check if the property is there, e.g.:

if(item && item.field && item.field.oneMoreField)
  return item.field.oneMoreField;

// or    
return item && item.field && item.field.oneMoreField;

Use a proxy object:

function safe(obj) {
  return new Proxy(obj, {
    get: function(target, name) {
      const result = target[name];
      if (!!result) {
        return (result instanceof Object)? safe(result) : result;
      }
      return safe({});
    }
  });
}
return safe(item.field.oneMoreField);

Or with a library, such as Lodash:

_.get(item, 'field.oneMoreField')

Angular ngrx: check is field exists in object

1 Answers1