Don't attempt wasm-bindgen install if it exists in path.

src/bindgen.rs

@@ -1,10 +1,19 @@
 use console::style;
 use emoji;
 use error::Error;
-use std::process::Command;
+use std::{env, fs, process::Command};
 use PBAR;
 
+#[cfg(target_family = "windows")]
+static PATH_SEP: &str = ";";
+
+#[cfg(not(target_family = "windows"))]
+static PATH_SEP: &str = ":";
+
 pub fn cargo_install_wasm_bindgen() -> Result<(), Error> {
+    if wasm_bindgen_installed()? {
+        return Ok(());
+    }
     let step = format!(
         "{} {}Installing WASM-bindgen...",
         style("[6/7]").bold().dim(),
@@ -71,3 +80,14 @@ pub fn wasm_bindgen_build(
         Ok(())
     }
 }
+
+fn wasm_bindgen_installed() -> Result<bool, Error> {
+    let path = env::var("PATH")?;
+    let is_installed = path.split(PATH_SEP)
+        .map(|p: &str| -> bool {
+            let prog_str = format!("{}/wasm-bindgen", p);
+            fs::metadata(prog_str).is_ok()
+        })
+        .fold(false, |res, b| res || b);
+    Ok(is_installed)
+}

src/error.rs

@@ -1,6 +1,7 @@
 //! Code related to error handling for wasm-pack
 use serde_json;
 use std::borrow::Cow;
+use std::env;
 use std::io;
 use toml;
 
@@ -13,6 +14,8 @@ pub enum Error {
     SerdeJson(#[cause] serde_json::Error),
     #[fail(display = "{}", _0)]
     SerdeToml(#[cause] toml::de::Error),
+    #[fail(display = "{}", _0)]
+    VarError(#[cause] env::VarError),
     #[fail(display = "{}. stderr:\n\n{}", message, stderr)]
     Cli { message: String, stderr: String },
 }
@@ -30,6 +33,7 @@ impl Error {
             Error::Io(_) => "There was an I/O error. Details:\n\n",
             Error::SerdeJson(_) => "There was an JSON error. Details:\n\n",
             Error::SerdeToml(_) => "There was an TOML error. Details:\n\n",
+            Error::VarError(_) => "There was an error finding an environment variable. Details:\n\n",
             Error::Cli {
                 message: _,
                 stderr: _,
@@ -55,3 +59,9 @@ impl From<toml::de::Error> for Error {
         Error::SerdeToml(e)
     }
 }
+
+impl From<env::VarError> for Error {
+    fn from(e: env::VarError) -> Self {
+        Error::VarError(e)
+    }
+}