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hugo-content/themes/cactus/exampleSite/content/posts/2019-03-08-es6-bind-trick.md

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+---
+title: Bind specific arguments of a function
+date: 2019-03-08 09:00:00
+tags:
+    - JavaScript
+category: tech
+keywords:
+    - Javascript
+    - ES2015
+    - ES6
+---
+
+To bind specific (nth) arguments of a function, we can write a decorator instead of using `Function.bind()`:
+
+```js
+function func(p1, p2, p3) {
+    console.log(p1, p2, p3);
+}
+// the binding starts after however many are passed in.
+function decorator(...bound_args) {
+    return function(...args) {
+        return func(...args, ...bound_args);
+    };
+}
+
+// bind the last parameter
+let f = decorator("3");
+f("a", "b");  // a b 3
+
+// bind the last two parameter
+let f2 = decorator("2", "3")
+f2("a");  // a 2 3
+```
+
+Even if we want to bind just the nth argument, we can do as follows:
+
+```js
+// bind a specific (nth) argument
+function decoratorN(n, bound_arg) {
+    return function(...args) {
+        args[n-1] = bound_arg;
+        return func(...args);
+    }
+}
+
+let fN = decoratorN(2, "2");
+fN("a","b","c"); // a 2 c
+```
+
+[https://stackoverflow.com/questions/27699493/javascript-partially-applied-function-how-to-bind-only-the-2nd-parameter](https://stackoverflow.com/questions/27699493/javascript-partially-applied-function-how-to-bind-only-the-2nd-parameter)