feat: new prefix option (#18)

Author: ybiquitous

README.md

@@ -40,7 +40,7 @@ b("element", { a: true, b: false, c: true });
 //=> "block__element--a block__element--c"
 ```
 
-### `elementDelimiter`
+### `elementDelimiter = "__"`
 
 ```ts
 const b = block("block", { elementDelimiter: "_" });
@@ -49,7 +49,7 @@ b("element");
 //=> "block_element"
 ```
 
-### `modifierDelimiter`
+### `modifierDelimiter = "--"`
 
 ```ts
 const b = block("block", { modifierDelimiter: "-" });
@@ -61,6 +61,18 @@ b("element", { a: true });
 //=> "block__element-a"
 ```
 
+### `prefix = ""`
+
+```ts
+const b = block("block", { prefix: "pre---" });
+
+b();
+//=> "pre---block"
+
+b("element", { a: true, b: true });
+//=> "pre---block__element--a pre---block__element--b"
+```
+
 ## Install
 
 ```sh

index.ts

@@ -2,14 +2,15 @@ type Modifiers = { [key: string]: boolean; };
 
 export default function bem(
   block: string,
-  { elementDelimiter = "__", modifierDelimiter =  "--" } = {},
+  { elementDelimiter = "__", modifierDelimiter =  "--", prefix = "" } = {},
 ) {
   return (elementOrModifiers?: string | Modifiers, modifiers?: Modifiers) => {
+    let base = `${prefix}${block}`;
+
     if (!elementOrModifiers) {
-      return block;
+      return base;
     }
 
-    let base = block;
     let mods = modifiers;
 
     if (typeof elementOrModifiers === "string") {

test.ts

@@ -86,3 +86,32 @@ describe("`modifierDelimiter` option", () => {
       .toBe("block__element-a block__element-c");
   });
 });
+
+describe("`prefix` option", () => {
+  const b = block("block", { prefix: "pre---" });
+
+  it("returns block", () => {
+    expect(b()).toBe("pre---block");
+  });
+
+  it("returns block with modifier", () => {
+    expect(b({ a: true, b: false })).toBe("pre---block--a");
+  });
+
+  it("returns block with multiple modifiers", () => {
+    expect(b({ a: true, b: false, c: true })).toBe("pre---block--a pre---block--c");
+  });
+
+  it("returns block with element", () => {
+    expect(b("element")).toBe("pre---block__element");
+  });
+
+  it("returns block with element and modifier", () => {
+    expect(b("element", { a: true, b: false })).toBe("pre---block__element--a");
+  });
+
+  it("returns block with element and multiple modifiers", () => {
+    expect(b("element", { a: true, b: false, c: true }))
+      .toBe("pre---block__element--a pre---block__element--c");
+  });
+});