flow like the river

VISUALIZACION/node_modules/math-expression-evaluator/src/postfix.js

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+
+var Mexp = require('./lexer.js');
+
+Mexp.prototype.toPostfix = function () {
+	'use strict';
+	var post = [], elem, popped, prep, pre, ele;
+	var stack = [{ value: "(", type: 4, pre: 0 }];
+	var arr = this.value;
+	for (var i = 1; i < arr.length; i++) {
+		if (arr[i].type === 1 || arr[i].type === 3 || arr[i].type === 13) {	//if token is number,constant,or n(which is also a special constant in our case)
+			if (arr[i].type === 1)
+				arr[i].value = Number(arr[i].value);
+			post.push(arr[i]);
+		}
+		else if (arr[i].type === 4) {
+			stack.push(arr[i]);
+		}
+		else if (arr[i].type === 5) {
+			while ((popped = stack.pop()).type !== 4) {
+				post.push(popped);
+			}
+		}
+		else if (arr[i].type === 11) {
+			while ((popped = stack.pop()).type !== 4) {
+				post.push(popped);
+			}
+			stack.push(popped);
+		}
+		else {
+			elem = arr[i];
+			pre = elem.pre;
+			ele = stack[stack.length - 1];
+			prep = ele.pre;
+			var flag = ele.value == 'Math.pow' && elem.value == 'Math.pow';
+			if (pre > prep) stack.push(elem);
+			else {
+				while (prep >= pre && !flag || flag && pre < prep) {
+					popped = stack.pop();
+					ele = stack[stack.length - 1];
+					post.push(popped);
+					prep = ele.pre;
+					flag = elem.value == 'Math.pow' && ele.value == 'Math.pow';
+				}
+				stack.push(elem);
+			}
+		}
+	}
+	return new Mexp(post);
+};
+module.exports = Mexp;