I have multiple types acceptable as a value in an object and one of them is array. When I get an array as parameter, I want to override it as a comma separated list. Apparently, after making sure the element I am trying to convert is indeed an array, Typescript returns a type related error:

for (const key in parameters) {
      if (Array.isArray(parameters[key])) {
        parameters[key] = parameters[key].join(',');
      }                                   ^^^^
                                         TS2339: Property 'join' does not exist on type

parameters type definition looks like this: parameters: Record<string, string | boolean | number | Array<string>

How can I get it to realize that the parameter is indeed an array in this context?

CodePudding user response：

Use another variable:

let parameters : Record<string, string | boolean | number | Array<string>> =
{
    's' : 1
}

for (const key in parameters) {
    let ass = parameters[key];
      if (Array.isArray(ass)) {
        parameters[key] = ass.join(',');
      }   
}

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