check input

package.json

@@ -3,6 +3,9 @@
   "version": "1.0.0",
   "main": "./lib/mathString.js",
   "license": "MIT",
+  "files": [
+    "libs"
+  ],
   "devDependencies": {
     "@types/jest": "^23.3.5",
     "husky": "^1.3.1",

src/checkPhrase.ts

@@ -0,0 +1,37 @@
+export const checkInput = (inp: string) => {
+  checkParenthesses(inp);
+  checkDot(inp);
+  checkOperator(inp, '\\/');
+  checkOperator(inp, '\\*');
+};
+
+const checkParenthesses = (inp: string) => {
+  const nOfOpenningParenhesses = numberOfChar(inp, '\\(');
+  const nOfClosingParenthesses = numberOfChar(inp, '\\)');
+  if (nOfClosingParenthesses !== nOfOpenningParenhesses) {
+    throw new Error('number of opening and closing parenthesses are not equal');
+  }
+};
+const numberOfChar = (inp: string, char: string) => {
+  const regExString = new RegExp(`${char}`, 'g');
+  const res = inp.match(regExString);
+  return res ? res.length : 0;
+};
+const checkUseMoreThanOne = (inp: string, char: string) => {
+  const regExString = new RegExp(`${char}{2,}`, 'g');
+  const res = inp.match(regExString);
+  return res ? res.length : 0;
+};
+const checkDot = (inp: string) => {
+  const res = checkUseMoreThanOne(inp, '\\.');
+  if (res > 0) {
+    throw new Error('the dot is used more than one in one place');
+  }
+};
+const checkOperator = (inp: string, operator: string) => {
+  if (checkUseMoreThanOne(inp, operator) > 0) {
+    throw new Error(
+      `the ${operator.replace(/[*/]/g, '')} is used more than one in one place`
+    );
+  }
+};