How to add item dynamically to tuple in TypeScript?

Question

this question comes from How to push item to [string] in TypeScript

I want to create function like below.

declare var sqlitePlugin:any;

getItems(options, callback) {

  var query: string = `SELECT item_code,
                        item_name
                      FROM items `;

  var param: [string];

  if (options['limit']) {
    var limit = options['limit'];
    query = query + " LIMIT ? ";
    param.push(String(limit));
  }

  if (options['offset']) {
    var offset = options['offset'];
    query = query + " OFFSET ? ";
    param.push(String(offset));
  }

  this.execQuery(query, param, (resultSet)=>{
    this.items = [];
    for(let i = 0; i < resultSet.rows.length; i++) {
      var item: Item = new Item();
      item.code = resultSet.rows.item(i).item_code;
      item.name = resultSet.rows.item(i).item_name;
      this.artists.push(item);
    }
    callback(this.items);
  } );
}

execQuery function needs to be set 'param' parameter as type of [string].

So I declared 'param' tuple as [string].

I want to change param tuple dynamically by options['limit'] and options['offset'] value.

But param.push(String(limit)); fails because param is undefined so I tried var param: [string] = []; then syntax error occurred.

[ts] Type 'undefined[]' is not assignable to type '[string]'. Property '0' is missing in type 'undefined[]'.

How do I solve this problem?

Thanks in advance.

chrisbajorin · Accepted Answer · 2016-05-27 01:59:03Z

1

If you truly want to have a single element tuple, you need just assign it instead of using push:

let param: [string];

if (options['limit']) {
    let limit = options['limit'];
    query = query + " LIMIT ? ";
    param = [String(limit)];
}

But this won't allow you to have both an offset and a limit. You probably want:

 let param: string[] = []

while using .push()

answered May 27, 2016 at 1:59

chrisbajorin

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2 Comments

raimtoon Over a year ago

thanks. I need to use [string] type because plugin function's design and dynamically add tuple item depends on number of options. ex) [10, 20], [10], [20]

chrisbajorin Over a year ago

Then it's just an array, not a tuple. Javascript doesn't support tuples. Typescript treats certain arrays as a specified number of elements, only governed by the typescript compiler. It will warn you, but it won't prevent you from doing anything. If a plugin says it's requiring a tuple, it's still just an array. If you're consuming this plugin, just pass an array. If you're producing it, you've chosen the wrong data structure.

Zen · Accepted Answer · 2016-05-27 01:48:10Z

0

Use var params: string[] = []; When you use statement var param: string[];, you only declare its type, params is undefined.
Don't use var.

answered May 27, 2016 at 1:48

Zen

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1 Comment

raimtoon Over a year ago

thanks, but execQuery needs to set [string] as param parameter.

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