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1 files changed, 26 insertions, 0 deletions

diff --git a/ts/thinking-about-unions/left-pad.ts b/ts/thinking-about-unions/left-pad.ts
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+++ b/ts/thinking-about-unions/left-pad.ts
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+/* 
+
+A stupidly simple example of unions.
+
+Unions can be used to describe a type that is actually several different types.
+Here, the Padding type is a union of either a number or a string. 
+Then, leftPad uses the union type so that it can accept either sort of type.
+
+*/
+
+type Padding = number | string;
+
+const leftPad = (value: string, padding: Padding) => {
+    if (typeof padding === 'number') {
+        return Array(padding + 1).join(' ') + value; // 0 indexing is for computers, this function is for people.
+    }
+    if (typeof padding === 'string') {
+        return padding + value;
+    }
+    throw new Error(`Expected number or string, got '${padding}'.`);
+}
+
+const marioMsg = 'It is I, Mario!';
+console.log(leftPad(marioMsg, 4));
+console.log(leftPad(marioMsg, "****"));
+console.log(leftPad(marioMsg, true));
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