Dictionary Syntax Error in Google Apps Script - dictionary

Question

I have a function that creates a dictionary based on a series of values from a sheet. I then try to pull one of the values from that sheet using a key. It works fine to log to the console. However, in an if statement, it says syntax error and nothing else. I cannot figure it out. Here is the function and the code that crashes. This problem only occurs in the for loop, and does not occur outside of it.
//creates dictionary
function columnLocationWithNotation(notation) {
var spreadsheet = SpreadsheetApp.openByUrl();
var sheet = spreadsheet.getActiveSheet();
var data = sheet.getDataRange();
var cells = data.getValues();
var dictionary = {};
switch (notation) {
case "zeroIndex":
for (var i = 0; i < sheet.getLastRow(); i++) {
dictionary[cells[i][0]] = cells[i][1]
}
return dictionary
break;
case "regularIndex":
for (var i = 0; i < sheet.getLastRow(); i++) {
dictionary[cells[i][0]] = cells[i][2]
}
return dictionary
break;
case "string":
for (var i = 0; i < sheet.getLastRow(); i++) {
dictionary[cells[i][0]] = cells[i][3]
}
return dictionary
break;
}
}
var master0indexDictionary = columnLocationWithNotation("zeroIndex")
for (var i = 1; i =< (sheet.getLastRow() - 1); i++) {
var phone = master0indexDictionary["Tutor Name"]
if (cells[i][phone] === phoneNumber) { //LINE WITH SYNTAX ERROR
//do something
}

Answer 1

It's not the highlighted line that is causing the problem, even though there are many other issues with your script. There's no '=<' operator in JavaScript. Use '<=' instead:
for (var i = 1; i <= (sheet.getLastRow() - 1); i++) {
Also, as Tanaike pointed out, your 'cells' variable is only defined in the context of your 'columnLocationWithNotation(notation)' function and will not be accessible from the global context. Globally-defined variables are visible from the functions you declare inside the global object, but not vice versa. Same applies to the 'sheet' variable. The 'phoneNumber' variable doesn't seem to be defined, at least not in the snippet of code you provided.
Note that putting 'break' after 'return' statements is redundant.
return dictionary;
break;
You can just return out of 'switch' statement without using breaks, or leave the breaks and put a single 'return' statement after 'switch'.
Finally, always put a semicolon at the end of the line. Doing so will help you avoid many potential pitfalls and issues with JS parser. I noticed several instances where you omitted the semicolon:
return dictionary
break;
var phone = master0indexDictionary["Tutor Name"]
For example, the following code will break if you don't have a habit of putting the semicolon in its rightful place
var a = {name: 'John'} //no semicolon
[a].forEach(function(element) {
Logger.log(element); //logs undefined
})
The JS parser treats this code as one line, so 'a' will still be 'undefined' by the time you call the 'forEach()' loop on the array.