javascript - Handling (type | undefined) checks in interfaces with Typescript -


here, i'm trying check if there's "booster" (card[]) in boosterstogo variable in player interface. if there is, want shift() , make currentbooster.

however, typescript giving me error:

message: 'type 'card[] | undefined' not assignable type 'card[]'. type 'undefined' not assignable type 'card[]'.'

my editor (vscode) underlining player.currentbooster in red here. what's going on? have had similar issues before using typescript have hacked around them little bit. what's proper way deal this?

if (player.boosterstogo.length > 0) {     player.currentbooster = player.boosterstogo.shift() } //player guaranteed fit interface player because that's what's explicitly passed function  export interface player {     boosterstogo: card[][]     currentbooster: card[]     picks: card[][]     human: boolean }  export interface card {     name: string     manacost: string     colors?: string[]     cmc: number     types: string[]     rarity: string     imageurl: string     pick?: boolean }

thanks!

i not reproduce in http://www.typescriptlang.org, maybe it's related typescript / intellisense version, change lib.d.ts definitions.

it may worth trying run bigger portion of problematic code in there , see if problem persists. if doesn't, maybe upgrading latest typescript version or updating vscode help.

otherwise, can enforce type type assertion (casting):

if (player.boosterstogo.length > 0) {     player.currentbooster = player.boosterstogo.shift() card[]; }

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