build: speed up logic in Travis CI build steps

.travis.yml

@@ -21,54 +21,63 @@ cache:
   directories:
     - node_modules
 before_install:
+  - |
+    # Setup utility functions
+    function node_version_lt () {
+      [[ "$(v "$TRAVIS_NODE_VERSION")" -lt "$(v "${1}")" ]]
+    }
+    function npm_module_installed () {
+      npm -lsp ls | grep -Fq "$(pwd)/node_modules/${1}:${1}@"
+    }
+    function npm_remove_module_re () {
+      node -e '
+        fs = require("fs");
+        p = JSON.parse(fs.readFileSync("package.json", "utf8"));
+        r = RegExp(process.argv[1]);
+        for (k in p.devDependencies) {
+          if (r.test(k)) delete p.devDependencies[k];
+        }
+        fs.writeFileSync("package.json", JSON.stringify(p, null, 2) + "\n");
+      ' "$@"
+    }
+    function npm_use_module () {
+      node -e '
+        fs = require("fs");
+        p = JSON.parse(fs.readFileSync("package.json", "utf8"));
+        p.devDependencies[process.argv[1]] = process.argv[2];
+        fs.writeFileSync("package.json", JSON.stringify(p, null, 2) + "\n");
+      ' "$@"
+    }
+    function v () {
+      tr '.' '\n' <<< "${1}" \
+        | awk '{ printf "%03d", $0 }' \
+        | sed 's/^0*//'
+    }
   # Configure npm
   - |
     # Skip updating shrinkwrap / lock
     npm config set shrinkwrap false
   # Setup Node.js version-specific dependencies
   - |
-    # eslint for linting
-    # - remove on Node.js < 8
-    if [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 8 ]]; then
-      node -pe 'Object.keys(require("./package").devDependencies).join("\n")' | \
-        grep -E '^eslint(-|$)' | \
-        xargs npm rm --save-dev
+    # Configure eslint for linting
+    if node_version_lt '8.0'; then npm_remove_module_re '^eslint(-|$)'
     fi
   - |
-    # istanbul for coverage
-    # - remove on Node.js < 0.10
-    if [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -eq 0 && "$(cut -d. -f2 <<< "$TRAVIS_NODE_VERSION")" -lt 10 ]]; then
-      npm rm --save-dev istanbul
+    # Configure istanbul for coverage
+    if node_version_lt '0.10'; then npm_remove_module_re '^istanbul$'
     fi
   - |
-    # mocha for testing
-    # - use 1.x for Node.js < 0.8
-    # - use 2.x for Node.js < 0.10
-    # - use 3.x for Node.js < 4
-    # - use 5.x for Node.js < 6
-    # - use 6.x for Node.js < 8
-    if [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -eq 0 && "$(cut -d. -f2 <<< "$TRAVIS_NODE_VERSION")" -lt 8 ]]; then
-      npm install --save-dev mocha@1.21.5
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -eq 0 && "$(cut -d. -f2 <<< "$TRAVIS_NODE_VERSION")" -lt 10 ]]; then
-      npm install --save-dev mocha@2.5.3
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 4 ]]; then
-      npm install --save-dev mocha@3.5.3
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 6 ]]; then
-      npm install --save-dev mocha@5.2.0
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 8 ]]; then
-      npm install --save-dev mocha@6.2.2
+    # Configure mocha for testing
+    if   node_version_lt '0.10'; then npm_use_module 'mocha' '2.5.3'
+    elif node_version_lt '4.0' ; then npm_use_module 'mocha' '3.5.3'
+    elif node_version_lt '6.0' ; then npm_use_module 'mocha' '5.2.0'
+    elif node_version_lt '8.0' ; then npm_use_module 'mocha' '6.2.2'
     fi
   - |
-    # supertest for http calls
-    # - use 1.1.0 for Node.js < 0.10
-    # - use 2.0.0 for Node.js < 4
-    # - use 3.4.2 for Node.js < 6
-    if [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -eq 0 && "$(cut -d. -f2 <<< "$TRAVIS_NODE_VERSION")" -lt 10 ]]; then
-      npm install --silent --save-dev supertest@1.1.0
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 4 ]]; then
-      npm install --silent --save-dev supertest@2.0.0
-    elif [[ "$(cut -d. -f1 <<< "$TRAVIS_NODE_VERSION")" -lt 6 ]]; then
-      npm install --save-dev supertest@3.4.2
+    # Configure supertest for http calls
+    if   node_version_lt '0.10'; then npm_use_module 'supertest' '1.1.0'
+    elif node_version_lt '4.0' ; then npm_use_module 'supertest' '2.0.0'
+    elif node_version_lt '6.0' ; then npm_use_module 'supertest' '3.4.2'
     fi
   # Update Node.js modules
   - |
@@ -81,15 +90,12 @@ before_install:
 script:
   - |
     # Run test script, depending on istanbul install
-    if npm -ps ls istanbul | grep -q istanbul; then
-      npm run-script test-travis
-    else
-      npm test
+    if npm_module_installed 'istanbul'; then npm run-script test-travis
+    else npm test
     fi
   - |
-    # Run linting, depending on eslint install
-    if npm -ps ls eslint | grep -q eslint; then
-      npm run-script lint
+    # Run linting, if eslint exists
+    if npm_module_installed 'eslint'; then npm run-script lint
     fi
 after_script:
   - |